Decorative light strings and repair device

ABSTRACT

One or more strings of decorative lights are supplied with power by converting a standard residential electrical voltage to a low-voltage, and supplying the low-voltage to at least one pair of parallel conductors having multiple decorative lights connected to the conductors along the lengths thereof, each of the lights, or groups of the lights, being connected in parallel across the conductors. A repair device for fixing a malfunctioning shunt across a failed filament in a light bulb in a group of series-connected miniature decorative bulbs includes a high-voltage pulse generator producing one or more pulses of a magnitude greater than the standard AC power line voltage. A connector receives the pulses from the pulse generator and supplies them to the group of series-connected miniature decorative bulbs. The pulse generator may be a piezoelectric pulse generator, a battery-powered electronic pulse generator, and/or an AC-powered electrical pulse generator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of PCT applicationPCT/US/02/07609 filed Mar. 13, 2002, claiming priority to U.S.provisional application 60/277,346 filed Mar. 19, 2001, 60/277,481 filedMar. 20, 2001, 60/287,162 filed Apr. 27, 2001, 60/289,865 filed May 9,2001, and U.S. application Ser. No. 09/854,255 filed May 14, 2001, Ser.No. 10/041,032 filed Dec. 28, 2001 and 10/068,452 filed Feb. 2, 2002.

FIELD OF THE INVENTION

The present invention relates to decorative lights, including lights forChristmas trees, including pre-strung or “pre-lit” artificial trees.

SUMMARY OF THE INVENTION

In accordance with the present invention, one or more strings ofdecorative lights are supplied with power by converting a standardresidential electrical voltage to a low-voltage, and supplying thelow-voltage to at least one pair of parallel conductors having multipledecorative lights connected to the conductors along the lengths thereof,each of the lights, or groups of the lights, being connected in parallelacross the conductors. A string of decorative lights embodying thisinvention comprises a power supply having an input adapted forconnection to a standard residential electrical power outlet, the powersupply including circuitry for converting the standard residentialvoltage to a low-voltage output; a pair of conductors connected to theoutput of the power supply for supplying the low-voltage output tomultiple decorative lights; and multiple lights connected to theconductors along the lengths thereof, each of the lights, or groups ofthe lights, being connected in parallel across the conductors. Thelights preferably require voltages of about 6 volts or less, and arepreferably connected in parallel groups of 2 to 5 lights per group withthe lights within each group being connected in series with each other.

The parallel groups are useful for current management. Light stringstypically have 100 bulbs, and 100 6-volt bulbs drawing 80 ma./bulb inparallel requires a total current flow of 8 amps, which requiresrelatively thick wires. With the series/parallel groups, the totalcurrent and the wire size can both be reduced.

In one particular embodiment, a low-voltage DC power supply is used incombination with a string having dual-bulb sockets and associated diodepairs to permit different decorative lighting effects to be achieved bysimply reversing the direction of current flow in the string, bychanging the orientation of the string plug relative to the powersupply.

Another aspect of the invention is to provide spare-part storage as anintegral part of the light string, so that failed bulbs and fuses can beeasily and quickly replaced with a minimum of effort. Improved bulbremoval devices are also provided to further facilitate bulbreplacement.

In accordance with another aspect of the present invention, there isprovided a repair device for fixing a malfunctioning shunt across afailed filament in a light bulb in a group of series-connected miniaturedecorative bulbs. The device includes a high-voltage pulse generatorproducing one or more pulses of a magnitude greater than the standard ACpower line voltage. A connector receives the pulses from the pulsegenerator and supplies them to the group of series-connected miniaturedecorative bulbs. The pulse generator may be a piezoelectric pulsegenerator, a battery-powered electronic pulse generator, and/or anAC-powered electrical pulse generator.

The group of series-connected miniature decorative bulbs is typicallyall or part of a light string that includes wires connecting the bulbsto each other and conducting electrical power to the bulbs. The repairdevice preferably includes a probe for sensing the strength of the ACelectrostatic field around a portion of the wires adjacent to the probeand producing an electrical signal representing the field strength. Anelectrical detector receives the signal and detects a change in thesignal that corresponds to a change in the strength of the ACelectrostatic field in the vicinity of a failed bulb. The detectorproduces an output signal when such a change is detected, and asignaling device connected to the detector produces a visible and/oraudible signal when the output signal is produced to indicate that theprobe is in the vicinity of a failed bulb. The failed bulb can then beidentified and replaced.

The repair device is preferably made in the form of a portable tool witha housing that forms at least one storage compartment so thatreplacement bulbs and fuses can be stored directly in the repair device.The storage compartment preferably includes multiple cavities so thatfuses and bulbs of different voltage ratings and sizes can be storedseparated from each other, to permit easy and safe identification ofdesired replacement components.

The housing also includes a bulb test socket connected to an electricalpower source within the portable tool to facilitate bulb testing. Afunctioning bulb inserted into the socket is illuminated, whilenon-functioning bulbs are not illuminated. A similar test socket may beprovided for fuses, with an indicator light signaling whether a fuse isgood or bad.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic diagram of a string of decorative lights embodyingthe present invention;

FIG. 2 is a more detailed diagram of the light string shown in FIG. 1;

FIG. 3 is an enlarged and more detailed perspective view of a portion ofthe light string of FIG. 2;

FIG. 4 is an exploded perspective view of a bulb and socket for use inthe light string of FIGS. 1-3;

FIG. 5 is a schematic circuit diagram of a suitable power supply for usein the light string of FIGS. 1-3;

FIG. 6 is a front elevation of a power supply for supplying multiplelight strings on a prelit artificial tree;

FIG. 7 is a side elevation of the power supply of FIG. 6;

FIG. 8 is a top plan view of the power supply of FIG. 6;

FIG. 9 is an exploded perspective view of a modified bulb and socket foruse in the light string of FIGS. 1-3;

FIG. 9 a is a schematic circuit diagram of a reversible DC power supplyfor use with the modified bulb and socket shown in FIG. 9;

FIG. 10 is an exploded perspective view of another modified bulb andsocket for use in the light string of FIGS. 1-3;

FIG. 11 is an exploded view of the bulb and socket shown in FIG. 10;

FIG. 12 is a perspective view of a tool for removing a failed bulb to bereplaced;

FIG. 13 is a side elevation of the tool of FIG. 12 being used to loosena bulb from its socket;

FIG. 14 is a side elevation of the tool of FIG. 12 being used to pry abulb out of its socket;

FIG. 15 is a schematic circuit diagram of a modified power supply foruse with the light string of FIGS. 1-3;

FIG. 16 is a perspective view of a power supply housing mounted on aprelit artificial tree for supplying power to multiple light strings onthe tree;

FIG. 17 is a perspective view of a decorative light string embodying theinvention;

FIG. 18 is a top view of the electrical plug included in the lightstring of FIG. 17;

FIG. 19 as a left end view of the electrical plug of FIGS. 17 and 18;

FIG. 20 is a side elevation view of the electrical plug of FIGS. 17 and18;

FIG. 21 is a left end view of a first alternative embodiment of anelectrical plug in which a semi-circular lamp remover is formed in thebody of the plug;

FIG. 22 is a left end view of a second alternative embodiment of anelectrical plug in which the body of the plug and the cover form acircular lamp remover;

FIG. 23 is a left end view of a third alternative embodiment of anelectrical plug in which the cover is slidably retained in channels onthe body of the plug;

FIG. 24 is a side elevation view of a fourth alternative embodiment ofan electrical plug in which the compartment is a separate component thatis attached to a conventional electrical plug;

FIG. 25 is a side elevation view of another alternative embodiment inwhich the compartment is attached to a receptacle instead of a plug;

FIG. 26 is a plan view of another alternative embodiment of a storagecompartment that can be attached to a plug, receptacle or wires of alight string;

FIG. 27 is a plan view of a modified version of the embodiment of FIG.26 in which the storage compartment accommodates two tiers ofreplacement components;

FIG. 28 is a side elevation of the storage compartment of FIG. 27 and alight-string plug to which the storage compartment is attachable;

FIG. 29 is a bottom perspective view of the storage compartment shown inFIG. 28;

FIG. 30 is a schematic diagram of a string of decorative lights beingplugged into a repair device embodying the present invention, with therepair device shown in side elevation with a portion of the housingbroken away to show the internal structure, portions of which are alsoshown in section;

FIG. 31 is a cross-sectional side view of a modified repair deviceembodying the invention;

FIG. 32 is a full side elevation of the device of FIG. 31, andillustrating a bulb being tested;

FIG. 33 a is a top plan view of the tool built into the tip of thedevice of FIG. 31, for assisting the removal of a failed bulb from alight string;

FIG. 33 b is a left end elevation of the tool shown in FIG. 33 a;

FIG. 33 c is a section taken along line 33 c-33 c in FIG. 33 a;

FIG. 33 d is a right end elevation of the tool shown in FIG. 33 a;

FIG. 33 e is a side elevation of the tool shown in FIG. 33 a;

FIG. 33 f is a top plan view of the tool shown in FIG. 33 a and a lightbulb, illustrating the use of the smaller arcuate recess to pry the bulbfrom its socket;

FIG. 33 g is a top plan view of the tool shown in FIG. 33 a and a lightbulb, illustrating the use of the larger arcuate recess to pry the bulbfrom its socket;

FIG. 33 h illustrates a cross-sectional view of the tool shown in FIG.33 a and a light bulb, illustrating the use of the aperture in the toolto remove the light bulb from its socket;

FIG. 34 is schematic circuit diagram of a piezoelectric high-voltagepulse source, dual sensitivity electrostatic field detector, bulbtester, fuse tester and continuity detector for use in the device ofFIGS. 30-33;

FIG. 35 is a schematic diagram of a battery-powered circuit forgenerating high-voltage pulses in the device of FIGS. 30-33;

FIG. 36 a is a schematic diagram of a simplified version of the circuitof FIG. 34 for detecting failed bulbs;

FIG. 36 b is a schematic diagram of a power source and bulb tester foruse with the circuit of FIG. 36 a;

FIG. 37 a is a block diagram of a modified circuit for detecting failedbulbs;

FIG. 37 b is a schematic diagram of a circuit for implementing the blockdiagram of FIG. 37 a;

FIG. 38 is a schematic diagram of an alternative battery-powered circuitfor generating high-voltage pulses;

FIG. 39 is a schematic diagram of another alternative battery-poweredcircuit for generating high-voltage pulses;

FIG. 40 is a schematic diagram of yet another alternative circuit forgenerating high-voltage pulses, using power from a standard AC outlet;

FIG. 41 is a schematic diagram of another alternative battery-poweredcircuit for generating high-voltage pulses;

FIG. 42 is a schematic diagram of an AC source for generatinghigh-voltage pulses;

FIG. 43 is a schematic diagram of another alternative circuit forgenerating high-voltage pulses, using power from a standard AC outlet;

FIG. 44 is a front perspective view of another modified repair deviceembodying the invention;

FIG. 45 is a back perspective view of the embodiment shown in FIG. 44;

FIG. 46 a is a right side elevation of the embodiment shown in FIGS. 44and 45;

FIG. 46 b is a front elevation of the embodiment shown in FIG. 46 a;

FIG. 47 a is a left side elevation with a partial cutout exposing someof the internal parts of the embodiment shown in FIGS. 44-46;

FIG. 47 b is a back elevation of the embodiment shown in FIG. 47 a;

FIG. 48 a is a top plan view of the embodiment shown in FIGS. 44-47;

FIG. 48 b is a bottom plan view of the embodiment shown in FIGS. 44-47;

FIG. 49 a is a right side elevation of the embodiment shown in FIGS.44-47, with the storage compartment cover removed;

FIG. 49 b is a plan view of the interior surface of the cover removedfrom the device as shown in FIG. 49 a;

FIG. 50 is a side elevation of the battery-containing andswitch-actuating element of the embodiment shown in FIGS. 44-47;

FIG. 51 a is an exploded right side elevation of the left-hand and uppersegments of the body portion of the embodiment shown in FIGS. 44-47;

FIG. 51 b is a side elevation of the trigger element of the embodimentshown in FIGS. 44-47;

FIG. 52 is a top plan view of the embodiment shown in FIGS. 44-47, witha portion broken away to show the internal structure;

FIGS. 53-54 are the actual shapes of pulses produced by pulse-generatingdevices for use in repair devices embodying the invention; and

FIG. 55 is a schematic circuit diagram of a modified power supply foruse with the light string of FIGS. 1-3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Although the invention will be described next in connection with certainpreferred embodiments, it will be understood that the invention is notlimited to those particular embodiments. On the contrary, thedescription of the invention is intended to cover all alternatives,modifications, and equivalent arrangements as may be included within thespirit and scope of the invention as defined by the appended claims.

Turning now to the drawings and referring first to FIGS. 1-3, a powersupply 10 is connected to a standard residential power outlet thatsupplies electrical power at a known voltage and frequency. In theUnited States, the known voltage is 120 volts and the frequency is 60Hz, whereas in Europe and some other countries the voltage is 220-250volts and the frequency is 50 Hz. The power supply 10 converts thestandard power signal to a 24-volt, 30-KHz pulse width modulatedwaveform (PWM), which is supplied to a pair of parallel conductors 11and 12 that supply power to multiple 6-volt incandescent lights L. Atypical light “string” contains 100 lights L.

Multiple groups of the lights L are connected across the two conductors11 and 12, with the lights within each group being connected in serieswith each other, and with the light groups in parallel with each other.For example, lights L1-L4 are connected in series to form a first lightgroup G1 connected across the parallel conductors 11 and 12, lightsL5-L8 are connected in series to form a second group G2 connected acrossthe conductors 11 and 12 in parallel with the first group G1, and so onto the last light group Gn.

If one of the bulbs fails, the group of four series-connected lightscontaining that bulb will be extinguished, but all the other 96 lightsin the other groups will remain illuminated because their power-supplycircuit is not interrupted by the failed bulb. Thus, the failed bulb canbe easily and quickly located and replaced. Moreover, there is no needfor shunts to bypass failed bulbs, which is a cost saving in themanufacture of the bulbs. If it is desired to avoid extinguishing allthe lights in a series-connected group when one of those lights fails,then the lights may still be provided with shunts that are responsive tothe low-voltage output of the power supply. That is, each shunt isinoperative unless and until it is subjected to substantially the fulloutput voltage of the power supply, but when the filament associatedwith a shunt fails, that shunt is subjected to the full output voltage,which renders that shunt operative to bypass the failed filament. Avariety of different shunt structures and materials are well known inthe industry, such as those described in U.S. Pat. Nos. 4,340,841 and4,808,885.

As shown in FIG. 4, each of the individual lights L uses a conventionalincandescent bulb 20 attached to a plastic base 21 adapted to beinserted into a plastic socket 22 attached to the wires that supplypower to the bulb. Each bulb contains a filament 23 that is held inplace by a pair of filament leads 25 and 26 extending downwardly througha glass bead 24 and a central aperture in the base 21. The lower ends ofthe leads 25, 26 are bent in opposite directions around the lower end ofthe base 21 and folded against opposite sides of the base to engagemating contacts 27 and 28 in the socket 22. The interior of the socket22 has a shape complementary to the exterior shape of the lower portionof the bulb base 21 so that the two components fit snugly together.

As shown most clearly in FIG. 4, the contacts 27 and 28 in each bulbbase 22 are formed by tabs attached to stripped end portions of themultiple wire segments that connect the lights L in the desiredconfiguration. These wire segments include multiple segments of theconductors 11 and 12 from FIGS. 1-3. As can be seen in FIG. 4, theconnector tabs 27, 28 in each socket 22 are fed up through a hole in thesocket and seated in slots formed in the interior surface of the socketon opposite sides of the hole. Prongs 27 a and 28 a on the sides of thetabs engage the plastic walls of the slots to hold the tabs securely inplace within the slots. When the bulb base 21 is inserted into itssocket 22, the bent filament leads 25, 26 on opposite sides of the bulbbase 21 are pressed into firm contact with the mating tabs 27, 28.

As can be most clearly seen at the lower right-hand corner of FIG. 4,the tab 27 at each end of each series-connected group G is connected totwo wires, one of which is a segment of one of the conductors 11 and 12,and the other of which leads to the next light in that particularseries-connected group G.

After all the connections have been made, the wires are twisted orwrapped together as in conventional light sets in which all the lightsare connected in series.

Turning next to the power supply 10 (shown in FIG. 1), a switching powersupply is preferred to minimize size and heat. Power supplies of thistype generally use switching technology to make the device smaller. Analternative is a power supply that uses switching technology and pulsewidth modulation or frequency modulation for output regulation, althoughthis type of power supply is generally more expensive than those usingelectronic transformers. One suitable electronic transformer isavailable from ELCO Lighting of Los Angeles, Calif., Cat. No. ETR150,which converts a 12-volt, 60-Hz input into a 12-volt, 30-KHz output.

FIG. 5 is a generalized schematic diagram of a power supply forconverting a standard 120-volt, 60-Hz input at terminals 30 and 31 intoa 24-volt AC output at terminals 32 and 33. It will be understood thatdevices for supplying low-voltage, high-frequency signals are well knownand vary to some degree depending on the output wattage range of thesupply, and the particular design of the device is not part of thepresent invention. FIG. 5 illustrates a standard self-oscillatinghalf-bridge circuit in which two transistors Q1 and Q2 and paralleldiodes D10 and D11 form the active side of the bridge, and twocapacitors C1 and C2 and parallel resistors R11 and R12 form the passiveside.

The AC input from terminals 30 and 31 is supplied through a fuse F1 to adiode bridge 34 consisting of diodes D1-D4 to produce a full-waverectified output across busses 35 and 36 leading to the transistors Q1,Q2 and the capacitors C1, C2. The capacitors C1, C2 form a voltagedivider, and one end of the primary winding T1 a of an outputtransformer T1 is connected to a point between the two capacitors. Thesecondary winding T1 b of the output transformer is connected to theoutput terminals 32, 33, which are typically part of a socket forreceiving one or more plugs on the ends of light strings. The resistorsR11 and R12 are connected in parallel with the capacitors C1 and C2 toequalize the voltages across the two capacitors, and also to provide acurrent bleed-off path for the capacitors in the event of a malfunctionor a blown fuse.

When power is supplied to the circuit, a capacitor C3 begins charging tothe input voltage through a diode D5. A diac D6 and a current-limitingresistor R1 are connected in series from a point between the capacitorC3 and the diode D5 to the base of the transistor Q2. When the capacitorC3 charges to the trigger voltage of the diac D6, the capacitor C3discharges, supplying current to the base of the transistor Q2 andturning on that transistor. A diode D7 avoids any circuit imbalancebetween the drive of Q1 and Q2 when the converter is in the steady-statemode, by preventing the capacitor from discharging and the diac fromtriggering. A resistor R2 limits the current from the buss 35. ResistorsR3 and R4 connected to the bases of the respective transistors Q1 and Q2stabilize the biases, and diodes D8 and D9 in parallel with therespective resistors R3 and R4 provide for fast turn off.

Self-oscillation of the illustrative circuit is provided by anoscillator transformer T2 having a saturable core. A ferrite core havinga B/H curve as square as possible is preferred to provide a reliablesaturation point. The number of turns in the primary and secondarywindings T2 a and T2 b of the transformer T2 are selected to force theoperating gain of the transistors Q1 and Q2, based on the followingequation:N _(p) *I _(p) −N _(s) *I _(s)where N_(p) is the number of turns in the primary winding T2 a, N_(s),is the number of turns in the secondary winding T2 b, I_(p) is the peakcollector current, and I_(s) is the base current. Suitable values forN_(p) and N_(s), are 1 and 3, respectively, and assuming a one-voltsupply across the primary winding N_(p), the forced gain is 3. Thenominal collector current I_(c), is:I _(c)=(P _(out)/η)*(2/V _(line))where P_(out) and V_(line) are RMS values, and η is the efficiency ofthe output transformer T1.

The saturable transformer T2 determines the oscillation frequency Faccording to the following equation:F=(V _(p)*10⁴)/(4*B _(s) *A*N _(p))where F is the chopper frequency, V_(p) is the voltage across theprimary winding T2 a of the oscillator transformer T2 in volts, B_(s) isthe core saturation flux in Tesla, and A is the core cross section incm².

The output transformer T1 has a non-saturable core with a ratioN_(p)/N_(s), to meet the output requirements, such as 24 volts (RMS). Itmust also meet the power requirements so that it may operate efficientlyand safely. The voltage across the primary winding T1 a is thepeak-to-peak rectified voltage V_(peak):V _(peak)=120*1.414=170 V _(peak)The desired 24-volt output translates to:V _(p-p)=24*2*1.414=67.8 V _(p-p)Thus, the required ratio of turns in the primary and secondary windingsof the transformer T1 is 170/67.8 or 2.5/1.

A third winding T1 c with a turns ratio of 10/1 with respect to theprimary winding provides a nominal 6-volt output for a bulb checker,described below.

The illustrative circuit also includes a light dimming feature. Thus, aswitch S1 permits the output from the secondary winding T1 b to be takenacross all the turns of that winding or across only a portion of theturns, from a center tap 37. A pair of thermistors RT1 and RT2 areprovided in the two leads from the secondary winding T1 b to theterminals 32 and 33 to limit inrush current during startup.

To automatically shut down the circuit in the event of a short circuitacross the output terminals 32 and 33, a transistor Q3 is connected toground from a point between the resistor R1 and the capacitor C3. Thetransistor Q3 is normally off, but is turned on in response to a currentlevel through resistor R13 that indicates a short circuit. The resistorR13 is connected in series with the emitter-collector circuits of thetwo transistors Q1 and Q2, and is connected to the base of thetransistor Q3 via resistors R14 and R15, a diode D12, and capacitor C4.The current in the emitter-collector circuit of transistors Q1 and Q2rises rapidly in the event of a short circuit across the outputterminals 32, 33. When this current flow through resistor R13 rises to alevel that causes the diode D12 to conduct, the transistor Q3 is turnedon, thereby disabling the entire power supply circuit.

The light string is preferably designed so that the load on the powersupply remains fixed so that there is no need to include voltage-controlcircuitry in the power supply to maintain a constant voltage withvariable loads. For example, the light string preferably does notinclude a plug or receptacle to permit multiple strings to be connectedtogether in series, end-to-end. Multiple strings may be supplied from asingle power supply by simply connecting each string directly to thepower supply output via parallel outlet sockets. Extra lengths of wiremay be provided between the power supply and the first light group ofeach string to permit different strings to be located on differentportions of a tree. Because ripple is insignificant in decorativelighting applications, circuitry to eliminate or control suchfluctuations is not necessary, thereby reducing the size and cost of thepower supply.

The low-voltage output of the power supply may have a voltage levelother than 24 volts, but it is preferably no greater than the 42.4 peakvoltage specified in the UL standard UL1950, SELV (Safe Extra-LowVoltage). With a 30-volt supply, for example, 10-volt lights may be usedin groups of three, or 6-volt lights may be used in groups of five.Other suitable supply voltages are 6 and 12 volts, although the numberof lights should be reduced when these lower output voltages are used.

The power supply may produce either a DC output or low-voltage ACoutputs. The frequency of a low-voltage AC output is preferably in therange from about 10 KHz to about 150 KHz within a 60 Hz envelope topermit the use of relatively small and low-cost transformers.

The voltage across each light must be kept low to minimize thecomplexity and cost of the light bulb and its socket. Six-volt bulbs arecurrently in mass production and can be purchased at a low cost perbulb, especially in large numbers. These bulbs are small and simple toinstall, and the low voltage permits the use of thin wire andinexpensive sockets, as well as minimizing the current in the mainconductors. In the illustrative light string of FIG. 1 with a 24-voltsupply and four lights per group, the voltage available for each lightis 6 volts. Consequently, the bulbs can be the simple and inexpensivebulbs that are mass produced for conventional Christmas light stringsusing series-connected lights. Similarly, the simple and inexpensivesockets used in such conventional Christmas light strings can also beused. Simple crimped electrical contacts may be provided at regularintervals along the lengths of the parallel conductors 11 and 12 forconnection to the end sockets in each group of four lights. The maximumcurrent level is only about 2 amperes in a 100-light string using four6-volt lights per group and a 24-volt supply, and thus the twoconductors 11 and 12 can also be light, thin, and inexpensive.

Light strings embodying the present invention are particularly usefulwhen used to pre-string artificial trees, such as Christmas trees. Suchtrees can contain well over 1000 lights and can cost several hundreddollars (US) at the retail level. When a single light and its shunt failin a series light string, the lights in an entire section of the treecan be extinguished, causing customer dissatisfaction and often returnof the tree for repair or replacement pursuant to a warranty claim. Whenthe artificial tree is made in sections that are assembled by theconsumer, only the malfunctioning section need be returned, but the costto the warrantor is nevertheless substantial. With the light string ofthe present invention, however, the only lights that are extinguishedwhen a single light fails are the lights in the same series-connectedgroup as the failed light. Since this group includes only a few lights,typically 2 to 5 lights, the failed bulb can be easily located andreplaced.

When pre-stringing artificial trees, the use of a single low-voltagepower supply for multiple strings is particularly advantageous becauseit permits several hundred lights to be powered by a single supply. Thisgreatly reduces the cost of the power supply per string, or per light,and permits an entire tree to be illuminated with only a few powersupplies, or even a single power supply, depending on the number oflights applied to the tree.

FIGS. 6-8 illustrate a single power supply 50 for supplying power to amultiplicity of light strings on a prelit artificial tree having ahollow artificial trunk 51. The power supply is contained in a housing52 having a concave recess 53 in its rear wall 54 to mate with the outersurface of the artificial trunk 51. A pair of apertured mounting tabs 55and 56 are provided at opposite ends of the rear wall 54 to permit thepower supply to be fastened to the trunk 51 with a pair of screws. Thepower input to the supply 50 is provided by a conventionalthree-conductor cord 57 that enters the housing through the bottom wall58. The free end of the cord 57 terminates in a standard three-prongplug.

The power output of the supply 50 is accessible from a terminal strip 59mounted in a vertically elongated slot 60 in the front wall of thehousing 52. This terminal strip 59 can receive a multiplicity of plugs61 on the ends of a multiplicity of different light strings, asillustrated in FIG. 7. Thus, if each light string contains 100 lightsand the terminal strip can receive ten plugs, the power supply canaccommodate a total of 1000 lights for a given tree. Each plug 61 isdesigned to fit the terminal strip 59 but not standard electricaloutlets, to avoid accidental attachment of the low-voltage light stringto a 120-volt power source. A latch 62 extends along one elongated edgeof the terminal strip 59 to engage each plug 61 as it is inserted intothe strip, to hold the plugs in place. When it is desired to remove oneof the plugs 61, a release tab 63 is pressed to tilt the latch enough torelease the plug.

The front wall of the power supply 50 also includes a bulb-testingsocket 64 containing a pair of electrical contacts positioned to makecontact with the exposed filament leads on a 6-volt bulb when it isinserted into the socket 64. The contacts in the socket 64 are connectedto a 6-volt power source derived from the power-supply circuit withinthe housing 52, so that a good bulb will be illuminated when insertedinto the socket 64.

If desired, dimmer, flicker, long-life and other operating modes can beprovided by the addition of minor circuitry to the power supply. In theillustrative power supply 50, a selector switch 65 is provided on thefront of the housing 52 to permit manual selection of such optionalmodes.

The front wall 60 of the housing 52 further includes an integratedstorage compartment 66 for storage of spare parts such as bulbs, toolsand/or fuses. This storage compartment 66 can be molded as a single unitthat can be simply pressed into place between flanges extending inwardlyfrom the edges of an aperture in the front wall 60 of the housing 52.The flange on the top edge of the aperture engages a slightly flexiblelatch 67 formed as an integral part of the upper front corner of thestorage compartment 66. The lower front corner of the compartment andthe adjacent flanges form detents 68 that function as pivot points toallow the storage compartment 66 to be pivoted in and out of the housing52, as illustrated in FIG. 7, exposing the open upper end of the storagecompartment.

As can be seen in FIG. 7, the bottom and rear walls 58 and 54 of thehousing 52 are preferably provided with respective holes 69 and 70 thatallow air to flow by convection through the housing to provide airflowdesired of the circuit elements within the housing.

FIG. 9 illustrates a modified bulb-socket construction for use with alow-voltage DC power supply. A DC power supply may be the same devicedescribed above with the addition of a full-wave rectifier at the outputto convert the low-voltage, high-frequency voltage to a low-voltage, DCvoltage. The plug on the light string to be connected to the DC powersupply is reversible so that the plug may be inserted into the socket ofthe power supply in either of two orientations, which will cause the DCcurrent to flow through the light string in either of two directions. Aswill be described in more detail below, the direction of the currentflow determines which of two bulbs in each of the multiple sockets alongthe length of the string are illuminated. This permits differentdecorative effects to be achieved with the same string by simplyreversing the orientation of the string plug relative to thepower-supply socket. For example, the bulbs illuminated by current flowin one direction may be clear bulbs, while the bulbs illuminated bycurrent flow in the opposite direction may be colored and/or flashingbulbs.

As can be seen in FIG. 9, each socket 100 forms receptacles 101 and 102for two different bulbs 103 and 104, respectively. For example, bulb 103may be clear and bulb 104 colored. Power is delivered to bothreceptacles 101 and 102 by the same pair of wires 105 and 106, but theconnector tabs 107 and 108 attached to the wires have increased widthsto permit electrical connection to the exposed filament leads on thebases of both bulbs. The rear connector tab 108 makes direct contactwith one of the filament leads on the base of each bulb. The frontconnector tab 107 carries a pair of inexpensive, oppositely poled,surface-mount diodes 109 and 110 having metallized contact surfaces 111and 112 at their upper ends. Each of the metallized contact surfaces 111and 112 makes contact with a filament lead on only one of the bulbbases, so that each diode 109 and 110 is connected to only one bulb.Because a diode conducts current in only one direction, and the twodiodes are poled in opposite directions, the DC current supplied to thesocket 100 will flow through only one of the two bulbs 103 or 104,depending upon the direction of the current flow, which in turn dependsupon the orientation of the string plug relative to the power-supplysocket.

As shown in FIG. 9, the two bulbs 103 and 104 preferably diverge fromeach other to reduce reflections from the non-illuminated bulb in eachpair. If desired, a non-reflective barrier may be provided between thetwo bulbs.

A modified construction is to provide only a single pair of diodes foreach of the parallel groups of lights. The diodes are provided at oneend of each parallel group, with two separate wires connecting eachdiode to one of the two bulbs in each socket in that group.

Another modified construction uses only a single bulb in each socket,with each bulb having two filaments and two diodes integrated into thebase of the bulb for controlling which filament receives power. The twofilaments are spaced from each other along the axis of the bulb, and oneend portion of the bulb is colored so that illumination of the filamentwithin that portion of the bulb produces a colored light, whileillumination of the other filament produces a clear light.Alternatively, the opposite end portions of the bulb can both becolored, but of two different colors.

FIG. 9 a is a diagram of a circuit for reversing the polarity of a DCpower supply. The standard AC power source is connected across a pair ofinput terminals 120 and 121 and full-wave rectified by a diode bridge122 as described above. The rectified output of the bridge 122 issupplied to the light string 123 connected to output terminals 124 and125. Between the bridge 122 and the terminals 124, 125, a dual poleswitch SW can change the direction of current flow so that the polarityof the terminals 124 and 125 is reversed.

FIGS. 10 and 11 illustrate a modified bulb base and socket constructionthat facilitates the replacement of a failed bulb. The bulb 130 in FIGS.10 and 11 has the same construction described above, including afilament 131 and a pair of filament leads 132 and 133 held in place by aglass bead 134. The leads 132 and 133 extend downwardly through a moldedplastic base 135 that fits into a complementary socket 136. In thismodified embodiment, the bulb base 135 includes a pair of diametricallyopposed lugs 137 and 138 that support a bulb-removal ring 139 betweenthe top surfaces of the lugs and the underside 140 of the flange 141 ofthe base 135. The central opening 142 of the ring 139 is dimensioned tohave a diameter just slightly smaller than that of the flange 141 sothat the ring can be forced upwardly over the lugs 137, 138 until thering 139 snaps over the top surfaces of the lugs, adjacent the undersideof the flange 141. The ring 139 is then captured on the base 135, butcan still rotate relative to the base.

To hold the bulb base 135 in the socket 136, the ring 139 forms ahinged, apertured tab 143 that can be bent downwardly to fit over alatching element 144 formed on the outer surface of the socket 136. Whenthe bulb fails, the tab 143 is pulled downwardly and away from thesocket 136 to release it from the socket 136, and then the tab 143 isused to rotate the ring 139 to assist in removing the bulb and its base135 from the socket 136. As the ring 139 is rotated, a descending ramp145 molded as an integral part of the ring engages a ramp 146 formed bya complementary notch 147 in the upper end of the socket 136. When thebulb base 135 and the socket are initially assembled, the ramp 145 onthe ring 139 nests in the complementary notch 147. But when the ring 139is rotated relative to the socket 136, the engagement of the two ramps145 and 146 forces the two parts away from each other, thereby liftingthe bulb base 135 out of the socket 136.

It is common to purchase Christmas lights a few strings at a time, andnew packages come with spare bulbs and fuses. However, as the lightstrings are used, the spare parts tend to become lost, and when they areneeded they cannot be found, or it becomes difficult to determine whichparts go with which string. Bulbs are made with a plethora of differentbases, bulb voltages, etc. and replacing a burned-out bulb with a bulbof the correct voltage, correct base type, and correct amperage fuse,not only assures optimum performance but also can be a safety factor.Some light strings are so inexpensive that the entire string can simplybe replaced when a bulb fails, but such re-purchases are furtherinconveniences. Failing to replace burned-out bulbs increases thevoltage to the other bulbs, which shortens the life of the remainingbulbs and accelerates the problem.

FIGS. 12-14 illustrate a separate bulb-removal tool 150 that can bepackaged with the other spare parts for a light string. The bases andsockets of such bulbs are typically made to fit tightly together toensure that the bulbs remain in their sockets and maintain theelectrical connections that are made by a tight frictional fit withinthose sockets. As a result, when a bulb fails, it is often difficult toremove the burned-out bulb for replacement. The tool 150 has anelongated tapered edge 151 that forms a cutout 152 that can be pressedbetween the top surface 153 of a bulb socket 154 and the lower surfaceof a flange 156 on a bulb base 157. The tool can be tilted up and down,and pivoted back and forth horizontally, while being pressed between theflange 156 and the socket surface 153, to initially loosen the bulb base157 in its socket 154 (see FIG. 13). The tool 150 can also be placedover the bulb 158, with the bulb extending upwardly through an opening159 in the tool, and with the inner edge 160 of the opening 159 restingon the top surface 153 of the socket 154, as illustrated in FIG. 14.With the tool 150 in this position, the tool is pulled upwardly to prythe bulb base 157 out of the socket 154. The tool 150 may be made ofmetal or a rigid plastic.

FIG. 15 is a generalized schematic diagram of a power supply forconverting a standard 120-volt, 60-Hz input at terminals 161, 162 into a24-volt AC output at terminals 163, 164 and 165, 166. This circuit usesa power switching supply to deliver a low-voltage, high-frequency PWMsignal while also providing the following features for the lightstrings:

-   -   continuous dimming capability from very low light level to full        light level,    -   multi-level dimming capability,    -   energy-saving and minimum-light-setting features,    -   soft-start feature to increase the lamp life,    -   soft start feature to reduce inrush current in the circuit, and    -   low cost with multi-feature lighting.

The AC input from the terminals 161, 162 is supplied through a fuse F21to a diode bridge DB21 consisting of four diodes to produce a full-waverectified output across buses 167 and 168, leading to a pair ofcapacitors C23 and C24 and a corresponding pair of transistors Q21 andQ22 forming a half bridge. The input to the diode bridge DB21 includes adual zener diode V_(Z21) and a pair of capacitors C21 and C22 which arepart of the radio frequency interference and line noise filteringcircuitry. Capacitors C25 and C26 are connected in parallel withcapacitors C23 and C24, respectively, to provide increased ripplecurrent rating and high-frequency performance. The capacitors C23 andC24 may be electrolytic capacitors while capacitors C25 and C26 arefilm-type capacitors offering high-frequency characteristics to theparallel combination. A pair of resistors R30 and R31 are connected inparallel with the capacitors C23 and C24, respectively, to equalize thevoltages across the two capacitors, and also to provide a currentbleed-off path for the capacitors in the event of a malfunction or ablown fuse.

The capacitors C23, C24 form a voltage divider, and one end of theprimary winding T_(p) of an output transformer T22 is connected to apoint between the two capacitors. The secondary windings T_(S21), andT_(S22) of the transformer T22 are connected to the output terminals163, 164 and 165, 166, which are typically part of a socket forreceiving one or more plugs on the ends of light strings. A capacitorC27 is connected in parallel with the primary winding T_(p) and acts asa snubber across the transformer T22 to reduce voltage ringing.

An integrated circuit driver IC21, such as a IR2153 driver availablefrom International Rectifier, drives the half bridge MOSFET transistorsQ21 and Q22. The power supply for the driver IC21 is derived from the DCbus through a resistor R25 and a parallel combination of capacitors C28and C29. The capacitor C28 is preferably an electrolytic capacitor, andthe capacitor C29 is preferably a film-type capacitor offeringhigh-frequency de-coupling characteristic to the driver IC21. A zenerdiode V_(Z22) clamps the voltage across the V_(CC) of the supply toensure a safe operating limit. The zener diode V_(Z22) along with theresistor R25 provide a regulated power supply for the driver IC21. Adiode D22 and a capacitor C31 provide a boot-strap mechanism for powerstorage to turn on the MOSFET Q21 of the half bridge.

The frequency of oscillation of the MOSFET driver is determined by thetotal resistance connected across pins 2 and 3 of the driver IC21 and acapacitor C30 connected across pin 3 and ground of the driver IC21. Thetwo outputs of the IC21 pins 7 and 5 are connected to the gates of theMOSFETs Q21 and Q22. A resistor R21 limits the gate current of theMOSFET Q21. A pair of resistors R22 and R24 are connected across theMOSFETs Q21 and Q22 to reduce noise sensitivity to avoid any spuriousturn-on of the MOSFETs. Resistor/capacitor combinations R27/C32 andR28/C33 are tied across the two MOSFETs Q21 and Q22 as snubbers toquench transient voltage surges at the turn-off of these transistors.

When power is applied to the circuit, the voltage developed on the bus167 causes voltage to be applied to the IC21 V_(CC). This causes thedriver IC21 to start oscillating and start driving the half-bridgetransistors Q21 and Q22 alternately. This applies voltage across theprimary winding T_(p) of the transformer T21, which in turn appliesvoltage across the secondary windings T_(S21) and T_(S22) of thetransformer, which is applied to the load.

The rectified output of the DC bus 167 is applied is applied to the Vccof the driver IC21 through a resistor R25. A zener diode V_(Z2) andcapacitors C28 and C29 are connected across the Vcc pin 1 of the driverIC21. The zener diode V_(Z2) provides regulation to the voltage appliedto the Vcc of the driver IC21. The two outputs of the IC21 pins 7 and 5are connected to the gates of the MOSFETs Q21 and Q22.

The output voltage can be varied by controlling the on/off ratio of thepulse width applied to the primary of the transformer T22. A limiteddimming control can be achieved by varying the frequency of theoscillation signal from the integrated circuit IC21. The output voltageis controlled by the potentiometer P1 connected to the integratedcircuit, which permits the user to adjust the light output to thedesired level.

The dimming feature can be used to provide different fixed light levels,such as a low light output, an energy-saving output, or a full-lightoutput. These three light levels can be achieved by use of three fixedresistors in place of the potentiometer P1. The three resistor settingscan be selected by use of a three-position switch. A low-light outputcorresponds to a minimum output voltage, and a full-light outputcorresponds to maximum output voltage. An energy-saving outputcorresponds to an intermediate light level such as a 75% light output.

The bulb life can be extended by soft starting the driver IC21, so thatthe IC starts with minimum light output and slowly ramps up to the fullor desired light level. At the time of start, the bulbs in the lightstring are normally cold, and the cold resistance of the bulbs is verylow. The cold resistance of a bulb is typically ten times lower than thesteady state, full-light operating resistance. If the full voltage wereapplied to a cold bulb at startup, the inrush bulb current could be tentimes the rated current of the bulb, which could cause the bulb filamentto weaken and ultimately break. By soft starting the control circuit,the voltage applied during starting of the bulb is significantly lower.As the bulb heats up and the bulb resistance increases, the voltage isincreased. Thus the bulb current never exceeds its hot rating, whichincreases bulb life.

Soft starting of the circuit also helps reduce the inrush current fromthe circuit, thereby avoiding any interaction with other circuits orappliances. Soft starting in this circuit can be achieved by startingthe driver IC21 at high frequency and then reducing it to the desiredoperating point with a small delay e.g. one second. This could beaccomplished in the circuit shown by adding a DC offset voltage to theground return of capacitor C30. This offset could be generated either bya time delayed voltage source derived from Bus 167 or a feedback loopdetecting the output current and maintaining a feedback voltage on C30ground return keeping the output current constant.

If a wider range of dimming control is needed, the driver IC21 can bereplaced by another integrated circuit, such as an IR21571, along with aPWM controller to drive the FETs, thereby providing a full range ofpulse width modulation. The output can be controlled from almost zerolight to full light.

The particular embodiment illustrated in FIG. 15 is a half bridgecircuit as an example for but it will be understood that the features ofthis circuit can be incorporated in other topologies such as flyback,forward, cuk, full bridge or other power converters, including isolatedas well as non-isolated power converter designs.

FIG. 16 illustrates a mounting arrangement for a housing 170 containingany of the power supplies described above, on a pre-lit artificial treehaving a central “trunk” pole 171 and multiple branches such as branches172-174 extending laterally from a support collar 175 on the pole 171.Each branch carries a portion of one of multiple light strings attachedto connectors on the housing 170. In the illustrative embodiment, twosuch connectors 176 and 177 project upwardly from the top of the housing170 for receiving mating connectors 178 and 179 attached to respectiveends of two pairs of conductors 180 and 181. When the connectors 178 and179 are mated to the connectors 176 and 177, the conductors areconnected to the power supply contained within the housing 170.

In an artificial tree having two or more vertical sections, the powersupply housing 170 is preferably mounted on the uppermost collar 175 inthe lowest of the three sections. Then one of the two connectors 176,177 can supply power to the lowest section(s) of the tree, whichgenerally is (are) the largest section(s), while the other connectorsupplies power to the smaller, upper sections of the tree. Theelectrical loads in the light strings in these two portions of the treeare typically about equal, and thus the output of the power supply canbe split evenly between the two output connectors 176, 177.

As can be seen in FIG. 16, the outer end panel 182 of the housing 170 ismost accessible to the user. This end panel 182 carries a manuallyoperated on-off switch 183 for turning the power supply on and off, andan indicator light 184 that is illuminated whenever the power supply isconnected to a power source. A dimmer knob 185 connected to thepotentiometer P1 permits the user to control the light level byadjusting the position of the potentiometer. A bulb socket 186 permitsthe user to test a bulb by connecting the bulb to an appropriate powersource within the housing. The panel 182 also contains a drawer 187 forstorage of spare bulbs and fuses. Power for the circuitry within thehousing 170 is supplied via cord 188.

To mount the housing 170 on the collar 175, a hook 189 extends upwardlyfrom the housing. The weight of the housing 170 forces the lower end ofthe inside panel 190 against the pole 171, and a yoke 191 projectingfrom the inside panel keeps the housing centered on the pole.

The two pairs of conductors 180 and 181 are connected to respectiveconnector blocks 192 and 193 each of which includes multiple connectorsfor receiving mating connectors crimped onto the ends of the wires ofmultiple light strings. For example, the connector block 193 typicallyreceives the connectors on a multiplicity of light strings mounted onthe bottom section(s) of a pre-lit tree. The other connector block 192typically receives a multiplicity of light strings for the middlesection of the tree. The top section(s) of the tree typically includestwo or more light strings, which are connected to a smaller thirdconnector block 196 connected to the block 192 via mating connectors 194and 195 on the ends of two pairs of conductors leading to the respectiveblocks 192 and 196.

FIG. 17 illustrates an electrical plug 210 that may be attached to oneend of the decorative light string to facilitate the storage of sparecomponents. This plug 210 is molded of an electrically non-conductivematerial such as plastic or a rubber compound. There are electricalprongs 212 that engage a socket. Alternatively the electrical plug canbe formed as a receptacle 211 (FIG. 25) on the female end or socket endof an electrical cord. There are two or more, commonly three, electricalwires 214 that connect to the prongs 212 or, in the case of a femaleplug, to the receptacles in the socket. Throughout this description, theterm “electrical plug” shall also mean an “electrical socket”. Theelectrical wires 214 have a plurality of electrical sockets 216connected to them. In the case of Christmas Lights, the electricalconnection is generally a series connection. Each socket 216 has a lamp218 mounted in it. There may be thirty-five to one hundred fifty lightsin a string of Christmas lights.

As seen in FIGS. 17 and 18, the molded plug 210 has a pair of opposedsidewalls 220, 222, a front wall 224 and a rear wall 226. Alternativelythe molded plug may be formed of other configurations such as a dome,cylinder or circle. Within the confines of the walls 220-226 is acompartment 228. The compartment 228 has a bottom 230. There is a cover232 that closes the top of the compartment 228. The cover 232 isattached to the sidewall 220 by means of a molded or living hinge 234.The living hinge 234 can be formed at the same time that the electricalplug 210 is molded. This minimizes the cost and number of componentsnecessary to attach the cover 232 to the sidewall 220. The cover 232 canbe made of clear plastic or colored plastic or rubber, depending on theneeds and desires of the manufacturer and user. The compartment isdimensioned to hold several spare lamps 236, spare fuses 238 and abulb-pulling tool.

The cover 232 can also be provided with a set of raised domes or bubblesthat are used to indicate light bulb voltage, amperage or otherinformation relating to the bulbs or fuses. By depressing theappropriate domes or bubbles, the user has a visual indication of thebulbs or fuses to buy for replacement items. Additional information suchas the number of lights in a string, the length of the string, the datepurchased or other such indications can also be added to the cover bysimilar indicia. Alternatively, the voltage, amperage or other importantinformation can be molded into the plug 210, the cover 232 or bottom 230when the parts are formed. This is a safety feature so that the useralways knows what size lamps and fuses he or she should be using with astring of lights.

In order to keep the cover 232 in a secure closed position on thecompartment 228, there is provided a latch means 240 on the top of theside wall 222. The latch can be a molded piece of rubber that engages anedge of the cover 232 opposite the living hinge. Instead of a latch, amagnetic strip may be added to the top of the sidewall 222 and acomplementary magnetic strip on the edge of the cover 232. Other closuredevices could be utilized as known in the art. It is preferable that thecover be water-resistant to keep water from entering the compartment 228and possibly damaging the spare lamps 236 or fuses 238.

As described above, there is provided a compartment 228 that is capableof storing spare lamps 236 and spare fuses 238 that is integral with themolded electrical plug 210. The spare components are readily accessiblewhen needed. The user merely opens the cover 228, removes the neededspare, and closes the cover. There is no searching for the whereaboutsof the spare parts bag or worrying about installing a wrong lamp orfuse. The current system of supplying the spare parts in a bag that isstapled to the wires between two of the bulbs also presents anothersafety issue. The staple can pierce the insulation and wire or canscratch the wire or the person removing the staple.

In FIG. 21, there is an alternative embodiment in which a semi-circularrecess 242 is formed in the front wall 224. The semi-circular recess 242forms an opening 244 that creates a lamp remover tool to remove burnedout lamps from their respective sockets. The diameter of the opening 244is substantially the same as the diameter of the base of the lamp 218.This allows the base of a burned out lamp 218 to be inserted into theopening 244 when the cover is opened. The cover is closed and held downby the user. This securely holds the lamp in the opening 244. The userthen pulls the socket 216 away from the lamp 218. Optionally the recess242 may have a metal insert 246 placed around its edge if the materialforming the front wall 224 is not strong enough to withstand the forcenecessary to remove the burned out lamp. The recess is illustrated inthe front wall 224 but can also be formed in the rear wall 226. A smallpiece of flexible material can also be formed on the cover or as part ofthe front wall 224 to partially or completely cover the opening 244.This keeps the spare lamps or fuses from falling out through the opening244.

FIG. 22 illustrates another alternative embodiment. The cover 228 isformed with a semi-circular dome 248 that aligns with the semi-circularrecess 242 in the front wall 224. The aligned dome 248 and recess 242form a circular opening 250. The dimension should be slightly smallerthan the diameter of the socket 216. When a burned out lamp 218 isinserted into the opening 250, the user holds the socket 216 in place.The lamp 218 is then pulled out from the socket 216. There is optionallyprovided a flexible webbed material 252 that has a plurality slitsemanating from the center of the opening 250 toward the circumference ofthe opening 250. This provides a covered opening that is easilypenetrated by a lamp 218 when it is inserted into the opening 250. Thewebbed material 252 can be easily formed with the cover 232 and frontwall 224.

FIG. 23 illustrates another alternative embodiment in which the cover232 is attached to the molded plug 210 by a different means. Instead ofusing a molded hinge 234, the cover 232 is held within a pair ofU-shaped channels 254, 256 extending along the top of the sidewalls 220,222. The U-shaped channels 254, 256 retain the edges of the cover 232 sothat the cover can be removed from the compartment 228 by sliding thecover 232 horizontally along the top of the compartment 228. The sametypes of lamp removers as described in the alternative embodiments shownin FIGS. 21 and 22 can be used with the embodiment shown in FIG. 23.

FIG. 24 illustrates another alternative embodiment in which acompartment 258 is formed as a separate stand-alone element. Thecompartment 258 can have the same features as the previously describedcompartment 228 such as different closure means and alternative lampremoval devices. However the compartment 258 has one or more open slots260 at its bottom. The slots 260 receive plastic closure devices 262such as conventionally used to secure bundles of wires together. Thesewire ties 62 securely hold the compartment 258 to the molded electricalplug 210. Other means such as clips or clamps can be used to attach thecompartment 258 to the plug 210. Such alternative fastening means willbe apparent to those skilled in the art. In this manner the compartments258 can be added to existing Christmas Light strings.

FIG. 25 illustrates another alternative embodiment in which the plug 210is replaced by a receptacle 211 having electrically conductive socketreceiving slots 213 to receive the electrical prongs 212. Thecompartment 258 is otherwise the same as described in FIG. 26 above. Thecompartment 258 is shown holding a bulb puller or bulb-removing tool268. Any of the plugs 210 described herein can be replaced by areceptacle 11 with all other features of the compartment remainingintact.

FIG. 26 illustrates a modified storage compartment 270 that providesmore organized storage of different types of replacement components.Three yokes 271, 272 and 273 extend upwardly from the bottom wall 274 ofthe compartment 270 to receive the tips of three replacement lamps 275,276 and 277, respectively. The open upper end of each of the yokes271-273 forms an opening that is slightly smaller than the minimumcross-sectional dimension of the lamp, and then flares out in thecentral portion of the yoke to approximately match the minimumcross-sectional dimension of the lamp. As a lamp is pressed down intothe open end of the yoke, the two arms of the yoke are forced slightlyapart to allow the lamp to enter, and then the arms spring back tocapture the lamp within the yoke as the lamp enters the wider centralportion of the opening in the yoke.

Near the right-hand side of the compartment as viewed in FIG. 26, a post278 extends upwardly from the bottom wall 274 to capture a replacementfuse 279 against the adjacent sidewall 280 of the compartment 270. Theside of the post 278 facing the sidewall 280 is undercut slightlybeneath its free end to capture the fuse 279 after it has been presseddown into the space between the post 278 and the sidewall 280,deflecting the resilient post 278 slightly away from the sidewall 280 inthe process.

The space between the post 278 and the end yoke 273 is utilized to storea lamp base 281 inserted between the post 278 and a second post 282extending upward from the bottom wall 274. The second post 82 positionsthe lamp base 281 between the fuse 278 and the lamp 277.

FIGS. 27-29 illustrate a modified storage compartment 290 that isdimensioned to receive two tiers of replacement components. The thickestcomponents are the lamp bases 291 and 292, which are much smaller attheir lower ends than at their upper ends. Thus, as can be seen in FIGS.27 and 28, they are stored with their small ends overlapping, so thatthe depth of the storage compartment need be increased by only about 50%to receive the two overlapping bases 291 and 292. This increase in depthis sufficient to accommodate two tiers of lamps and fuses.

As can be seen in FIGS. 28 and 29, the storage compartment 290 isprovided with two plastic prongs 293 and 294 formed as an integral partof the storage compartment and adapted to fit into the socket of astandard socket 295 on the end of a light string. Thus, the storagecompartment 290 can be removably attached to a light string by simplyplugging it into the socket typically provided on one end of a lightstring. In addition, as can be seen in FIG. 29, the plastic prongs 293and 294 form notches 293 a and 294 a so that the prongs can be clippedto the wires 296 and 297 of a light string. Each of the notches 293 aand 294 a has a narrow throat 293 b or 294 b at its open end to hold thestorage compartment 290 captive on the wires 296, 297 after the prongs293, 294 have been pressed onto the wires.

In the event of a failure of one or more bulbs in the decorative lightstring, the hand-held tool shown in FIGS. 30, 31-32 or 44-52 may be usedto identify, and often repair, the failed bulb(s). In the illustrativeembodiment shown in FIG. 30, a portable, hand-held housing 310 containsa conventional piezoelectric device 311 of the type used in lighters forgas grills, for example. The piezoelectric device 311 is actuated by arod 312 that extends out of the housing 310 into a finger hole 313 wherethe rod 312 is attached to a trigger 314. When the trigger 314 ispulled, the rod 312 is retracted and retracts with it the left-hand endof a compression spring 315 and a cam element 316. The compressionspring 315 is supported by a stationary rod 317 which telescopes insidethe retracting rod 312 while the spring 315 is being compressed againsta latch plate 318 at the right-hand end of the spring.

When the spring 315 is fully compressed, an angled camming surface 316 aon the cam element 316 engages a pin 318 a extending laterally from thelatch plate 318, which is free to turn around the axis of the rod 317.The camming surface 316 a turns the pin 318 a until the pin reaches alongitudinal slot 319, at which point the compression spring 315 isreleased to rapidly advance a metal striker 320 against a striker cap321 on one end of a piezoelectric crystal 322. The opposite end of thecrystal 322 carries a second metal cap 323, and the force applied to thecrystal 322 by the striker 320 produces a rapidly rising output voltageacross the two metal caps 321 and 323. When the trigger 314 is released,a light return spring 324 returns the striker 320 and the latch plate318 to their original positions, which in turn returns the cam element316, the rod 312 and the trigger 314 to their original positions.

Although the piezoelectric device is illustrated in FIG. 30 ascontaining a single crystal 322, it is preferred to use thosecommercially available devices that contain two stacked crystals. Thestriking mechanism in such devices strikes both crystals in tandem,producing an output pulse that is the sum of the pulses produced by bothcrystals. FIG. 53 illustrates a pulse generated by such a pulse sourceconnected to a 100-bulb light string with the first and last bulbsremoved to show the pulse that would be applied to a defective shunt.

The metal caps 321, 323 are connected to a pair of conductors 325 and326 leading to a socket 330 for receiving a plug 331 on the end of alight string 332. The conductor 326 may be interrupted by apulse-triggering air gap 329 formed between a pair of electrodes 327 and328, forming an air gap having a width from about 0.20 to about 0.25inch. The voltage output from the piezoelectric crystal 322 builds upacross the electrodes 327, 328 until the voltage causes an arc acrossthe gap 329. The arcing produces a sharp voltage pulse at the socket 330connected to the conductor 326, and in the light string 332 plugged intothe socket 330. The trigger 314 is typically pulled several times (e.g.,up to five times) to supply repetitive pulses to the light string.

Substantially the entire voltage of each pulse is applied to anyinoperative shunt in a failed bulb in the light string, because thefailed shunt in a failed bulb appears as an open circuit in the lightstring. The light string is then unplugged from the socket 330 andplugged into a standard AC electrical outlet to render conductive amalfunctioning shunt not repaired by the pulses. It has been found thatthe combination of the high-voltage pulses and the subsequentapplication of sustained lower-voltage power (e.g., 110 volts) repairs ahigh percentage of failed bulbs with malfunctioning shunts. When amalfunctioning shunt is fixed, electrical current then flows through thefailed bulb containing that shunt, causing all the bulbs in the lightstring except the failed bulb to become illuminated. The failed bulb canthen be easily identified and replaced.

The piezoelectric device 311 may be used without the spark gap 329, inwhich event the malfunctioning shunt itself acts as a spark gap. As willbe described in more detail below, the piezoelectric device may bereplaced with a pulse-generating circuit and an electrical power source.Circuitry may also be added to stretch the pulses (from any type ofsource) before they are applied to the light string so as to increasethe time interval during which the high voltage is applied to themalfunctioning shunt.

In cases where a hundred-light set comprises two fifty-light sectionsconnected in parallel with each other, each applied pulse is dividedbetween these two sections and may not have enough potential to activatea malfunctioning shunt in either section. In these cases, an additionaland rather simple step is added. First, any bulb from the workingsection of lights is removed from its base. This extinguishes the lightsin the working section and isolates this working section from the onewith the bad bulb. Next, the string of series-connected bulbs is pluggedinto the socket of the repair device, and the trigger-pulling procedureis repeated. The lights are then unplugged from the repair device, theremoved bulb is re-installed, and the light set is re-plugged into itsusual power source. Since the shunt in the bad bulb is now operative,all the lights except the burned out one(s) will become illuminated.

When a bulb does not illuminate because of a bad connection in the baseof the bulb, the pulse from the piezoelectric element will not fix/clearthis type of problem. Bad connections in the base and othermiscellaneous problems usually account for less than 20% of the overallfailures of light strings.

To offer the broadest range of capabilities, a modified embodiment ofthe present invention, illustrated in FIGS. 31-33 h, incorporates bothan open-circuit detection system and a bulb tester, thus providing theuser a complete light care system. The detection system in theillustrative device of FIGS. 31-33 h locates burned-out bulbs in astring that is plugged into a power source. A pair of batteries 340power a circuit 341 built into a housing 342 and connected to a probefor sensing an AC electrostatic field emanating from the light string.When the probe is moved along the light string, it alters the operationof the circuit 341, which in turn energizes a visual and/or audiblesignaling device such as a light-emitting diode (“LED”) 41 projectingthrough an aperture in the top wall of the housing 342. Another suitablesignaling device is a buzzer that can be energized by the circuit 341 toproduce a beeping sound, as will be described in more detail below.

The circuit 341 is activated by a spring-loaded switch 344 that connectsthe circuit 341 with the batteries 340 when depressed by the user. Thebatteries 340 remain connected with the circuit 341 only as long as theswitch 344 remains depressed, and are disconnected by the opening of thespring-loaded switch 344 as soon as the switch is released.

The circuit 341 includes a conventional oscillator and supplies acontinual series of pulses to the LED 41 as long as (1) the circuitremains connected to the batteries, and (2) the probe detects an ACelectrostatic field. As the detector is moved along the light stringtoward the burned-out bulb, the pulses supplied to the LED 41 cause itto flash at regular intervals. The same pulses may cause a buzzer tobeep at regular intervals. There is no need for the user to repeatedlypress and release the switch to produce multiple pulses as the detectortraverses the light string. As the detector passes the burned-out bulb,the open circuit created by that bulb greatly reduces the electrostaticfield strength, and thus the LED 41 is extinguished, indicating that theprobe is located near the bad bulb.

As can be seen in FIGS. 33 a-33 h, a tool 345 for facilitating removalof a burned-out bulb is mounted on the distal end of the housing 342. Inthe illustrative embodiment, the tool 345 is in the form of a flat bladehaving a front edge that forms a pair of arcuate recesses 345 a and 345b that mate with the interface between a bulb 346 and its socket 347.The smaller recess 345 a is flanked by a pair of tapered surfaces 345 cand 345 d that can be pressed into the bulb/socket interface topenetrate into that interface, as illustrated in FIG. 33 f, and thentwisted to pry the bulb out of its socket. After the interface has beenopened slightly, the larger recess 345 b can be pushed into theinterface to open it more widely, as illustrated in FIG. 33 g, and thentwisted or tilted to remove the bulb from its socket. A tapered tab 348at one end of the recess 345 b can be inserted into the interface andtwisted to pry the two parts away from each other. The central portionof the tool 345 forms an opening 349 shaped to permit the bulb 346 toextend through the blade, as illustrated in FIG. 33 h, with the wide endof the opening 349 fitting over a flange 346 a on the bulb base. A smalltab 349 a on the wide end of the opening 349 fits under a flange on thebulb base so that when the blade is pulled longitudinally away from thesocket 347, the bulb and its base can be pulled out of the socket. Thenarrow end of the opening 349 is curved out of the plane of the blade toform a cradle 349 b shaped to conform to the shape of the adjacentportion of the bulb, to avoid a sharp edge that might break the bulbwhile it is being extracted from its socket.

In a preferred electrostatic field detection circuit illustrated in FIG.34, the manually operated switch 344 applies power to the circuit whenmoved to the closed position where it connects a battery B to Vcc. Thebattery B applies a voltage V_(cc) to the LED 41 which is thenilluminated whenever it is connected to ground by a switching transistorQ41. The battery voltage V_(cc) also charges a capacitor C44 through aresistor R44. As the capacitor C44 charges, it turns on a transistorQ42, which pulls low the signal line between a pair of inverters U41 andU42 described below. The transistor Q42 turns off when the capacitor C44is charged. The momentary low produced during the time the transistorQ42 is on triggers a pair of oscillators also described below, causingthe LED 41 to flash to indicate that the circuit is energized, thebattery is good, and the circuit is functional.

The probe P of the detector is connected to a resistor R41 providing ahigh impedance, which in turn is connected to an HCMOS high-gaininverter U41 and a positive voltage clamp formed by a diode D41. Whenthe probe P is adjacent a conductor connected to an AC power source, theAC electrostatic field surrounding the conductor induces an AC signal inthe probe. This signal is typically a sinusoidal 60-Hz signal, which isconverted into an amplified square wave by the high-gain inverter U41.This square wave is passed through a second inverter U42, which chargesa capacitor C41 through a diode D42 and discharges the capacitor througha resistor R42. The successive charging and discharging of the capacitorC41 produces a sawtooth signal in a line 350 leading to a pair ofoscillators 351 and 352 via diode D43.

The signal that passes through the diode D43 triggers the oscillators351 and 352. The first oscillator 351 is a low-frequency square-waveoscillator that operates at ˜10 Hz and is formed by inverters U43 andU44, resistors R43 and R44 and a capacitor C42. The second oscillator352 is a high-frequency square-wave oscillator that operates at ˜2.8 kHzand is formed by inverters U45 and U46, resistors R45 and R46, and acapacitor C43. Both oscillators are conventional free-runningoscillators, and the output of the low-frequency oscillator 351 controlsthe on-time of the high-frequency oscillator 352. The modulated outputof the high-frequency oscillator 352 drives the transistor Q41, turningthe transistor on and off at the 25-Hz rate to produce visible blinkingof the LED 41. The high-frequency (2.8 kHz) component of the oscillatoroutput also drives a buzzer 353 connected in parallel with the LED 41,so that the buzzer produces a beeping sound that can be heard by theuser.

To locate a failed bulb, the switch 344 is held in the closed positionwhile the probe is moved along the length of the light string, keepingthe probe within one inch or less from the light string (the sensitivityincreases as the probe is moved closer to the light string). The LED 41flashes repetitively and the buzzer 353 beeps until the probe moves pastthe failed bulb, and then the LED 41 and the buzzer 353 are de-energizedas the probe passes the failed bulb, thereby indicating to the user thatthis is the location of the bulb to be replaced. Alternatively, the LED41 and the buzzer 353 will remain de-energized until the probe reachesthe failed bulb and then become energized as the probe passes the failedbulb or other discontinuity in the light string, again indicating thelocation of the defect.

This detection system is not sensitive to the polarization of theenergization of the light string while it is being scanned. Regardlessof the polarization, both the LED 41 and the buzzer 353 change, eitherfrom activated to deactivated or from deactivated to activated, as theprobe P moves past a failed bulb. Specifically, when the probe Papproaches the failed bulb along the “hot” wire leading to that bulb,the LED 41 flashes and the buzzer 353 beeps until the probe P reachesthe bad bulb, at which time the LED 41 is extinguished and the buzzer353 is silenced. When the probe P approaches the failed bulb along theneutral wire, the LED 41 remains extinguished and the buzzer 353 remainssilent until the probe P is adjacent the bad bulb, at which time the LED41 begins to flash and the buzzer 353 begins to beep. Thus, in eithercase there is a clear change in the status of both the LED 41 and thebuzzer 353 to indicate to the user the location of the bad bulb.

Another advantage of this detection system is that the automaticcontinuous pulsing of the LED 41 and the buzzer 353 provides both visualand audible feedback signals to the user that enable the user to judgethe optimum distance between the detector and the light string beingscanned. The user can move the detector toward and away from the lightstring while observing the LED 41 and listening to the buzzer todetermine the distance at which the visual and audible signals repeatconsistently at regular intervals.

To permit the sensitivity of the detector circuit to be reduced, aswitch S42 permits a capacitor C45 to be connected to ground from apoint between the resistor R41 and the inverter U41. This sensitivityadjustment is desirable because in the presence of a strongelectrostatic field from a nearby light string, the LED 41 may continueto flash and give false readings.

To permit the testing of bulbs with the same device that is used todetect burned-out bulbs, a bulb-testing loop 354 (FIGS. 31 and 32) isformed as an integral part of the housing 310. The inside surface of theloop 354 contains a pair of electrical contacts connected to the samebattery B (FIG. 34) that powers the detection circuit, to supply powerto the bulb being tested. These contacts are positioned to contact theexposed folded ends of the filament leads on opposite sides of the bulbbase when the bulb base is inserted into the loop. The loop 354 may bedesigned to accommodate the latest commercial miniature bulbs thatinclude a long tab on the bottom of the bulb base to maintaincreepage/clearance distances and push snow and dirt out of the socketwhen it is installed as specified in UL 588, Christmas-Tree andDecorative-Lighting Outfits, Sixteenth Edition. As seen in FIGS. 31 and32, the loop 354 is preferably placed on the top of the housing 310,although the location is not determinative of its function.

In operation, a bulb base is inserted into the loop 354 from the lowerend of the bulb base, and the tapered neck of the base extends all theway through the loop 354. The thickened section of the base limits theinsertion of the bulb. At this point, the filament leads exposed on thebase of the bulb engage the electrical contacts on the inside surface ofthe loop 354. Since the contacts have a battery voltage across them, thebulb will illuminate if it is good. If the bulb fails to illuminate, theuser can conclude that the bulb is no longer functional.

For the convenience of the user, the housing 310 further includes anintegrated storage compartment 400 (see FIG. 31) for storage of spareparts such as bulbs and/or fuses. This storage compartment 400 can bemolded into the housing 310. The cover 401 of the storage compartment310 may be made with an integrally molded living hinge 402 and anintegral latch 403. An example of an alternate construction would be asliding cover, instead of a hinged cover, over the compartment holdingthe spare parts. The storage compartment is preferably divided intomultiple cavities, as can be seen in FIG. 31, to permit differentcomponents to be separated from each other to facilitate retrieval ofdesired components.

A fuse-testing socket 355 may also be provided to permit the testing offuses as well as bulbs. In the illustrative circuit of FIG. 34, thefuse-testing socket is connected in series with the LED 41 and thebattery B, so that insertion of a good fuse into the socket 355illuminates the LED 41 as a good-fuse indicator, while a defective fusedoes not illuminate the LED 41.

The detection circuit of FIG. 34 also includes a continuity indicator toprovide the user with a visible indication when a bulb shunt has beenfixed by pulses from the piezoelectric device 311. Thus, a secondlight-emitting diode LED 42 (typically a green LED) is connected fromthe positive side of the battery B to one side of the socket 330 towhich the light string is connected. The piezoelectric device 311 andits spark gap 362 are connected across the socket 330 that receives theplug of the light string. It can be seen that the switch 344 isolatesthe piezoelectric circuit from the detection circuit so that thedetection circuit is protected from the high-voltage pulses that aregenerated to repair a malfunctioning shunt. When a malfunctioning shuntin the light string is repaired, current flows from the battery Bthrough LED 42 and the light string to ground, thereby illuminating LED42 to indicate to the user that the shunt has been fixed and continuityrestored in the light string.

When LED 42 illuminates, indicating that the shunt has been fixed, thelight string is then unplugged from the socket 330 and plugged into astandard AC outlet. All the bulbs in the light string will nowilluminate, with the exception of the failed bulb, which can be quicklydetected and replaced. If desired, the removed bulb can be tested in theloop 354 before it is replaced, to confirm that the failed bulb has beenproperly identified.

When the LED 42 does not illuminate after the trigger 314 has beenpulled several times, the user still unplugs the light string from thesocket 330 and plugs it into an AC outlet. As described above, thisadditional, sustained AC power may render operative a shunt not renderedoperative by the high-voltage pulses. In either event, the detector maybe used to locate the failed bulb if the shunt does not becomeoperative.

The high-voltage pulses used to fix a malfunctioning shunt in a failedbulb may be generated by means other than the piezoelectric sourcedescribed above. For example, the DC output of a battery may beconverted to an AC signal that is passed through a step-up transformerto increase the voltage level, rectified and then used to charge acapacitor that discharges across a spark gap when it has accumulated acharge of the requisite magnitude. The charging and discharging of thecapacitor continues as long as the AC signal continues to be supplied tothe transformer. The resulting voltage pulses are applied to a lightstring containing a failed bulb with a malfunctioning shunt, asdescribed above.

FIG. 35 illustrates a battery-powered circuit for generatinghigh-voltage pulses that may be used independently of, or in combinationwith, the piezoelectric device 311. The illustrative circuit includesthe piezoelectric pulse generator 311 described above, for producinghigh-voltage pulses across a failed bulb in a light string connectedacross terminals 360 and 361 in the socket 330. A diode D54 isolates thepiezoelectric device 311 from the rest of the circuit, which forms asecond high-voltage pulse source powered by a battery B. The spark gap362 that develops the threshold voltage for the pulse from thepiezoelectric device 311 is located between the terminal 361 and thedevice 311.

Before describing the pulse-generating circuit in FIG. 35, the overallsequence of operations for troubleshooting an extinguished light stringwill be described. The battery-powered pulse is produced by simplypressing a switch and holding it down until an LED51 glows brightly,indicating that a capacitor has been fully charged. A pulse from thepiezoelectric device 311 is produced by pulling the trigger 314 (asshown in FIG. 32) several times. If either type of pulse fixes amalfunctioning shunt in a failed bulb, an LED52 is illuminated. Ifeither type of pulse by itself does not fix a malfunctioning shunt, thetwo pulses can be generated concurrently, which will fix certain shuntsthat cannot be fixed by either pulse alone.

In general, there are four types of bulbs encountered in actualpractice. First, there are bulbs in which the shunt will be fixed byeither type of pulse by itself, and thus either the battery-poweredpulse or the piezoelectric pulse may be used for this purpose. Second,there are bulbs in which the shunt can be fixed only with thehigher-energy pulse produced by concurrent generation of both thebattery-powered pulse and the piezoelectric pulse. Third, there arebulbs in which the shunt cannot be fixed, but the failed bulb will glowwhen the battery-powered circuit constantly applies a high voltage tothe bulb; the switch is held down until the glowing bulb is visuallydetected. Fourth, there are bulbs that will not glow, but will blink orflash in response to the higher-energy pulse produced by concurrentgeneration of both the battery-powered pulse and the piezoelectricpulse; this pulse can be repeated until the defective bulb is detectedby visually observing its flash.

Returning now to FIG. 35, when the pulse from the piezoelectric device311 fixes the malfunctioning shunt, a green light-emitting diode LED52is illuminated by current flowing from the battery B through a diodeD55, the light string connected to terminals 360 and 361, and the LED52to ground. The diode D55 protects the remaining circuitry from thehigh-voltage pulses produced by the piezoelectric device 311. If theshunt is still not conductive after being pulsed by the piezoelectricdevice 311, current does not flow through the light string and thus theLED52 remains extinguished. Thus, LED52 acts as a continuity indicatorto provide the user with a visible indication of whether themalfunctioning shunt in the light string has been fixed.

The balance of the circuit shown in FIG. 35 generates thebattery-powered, high-voltage pulse. A switch S50 is pressed to connectthe battery (or batteries) B to a conventional ringing choke converteror blocking oscillator operating at a relatively low frequency, e.g.,6.5 kHz, under nominal load. The oscillator converts the 3-volt DCoutput of the battery B to an AC signal that is supplied to the primarywinding T50 a of a step-up transformer T50. The stepped-up voltage fromthe secondary winding T50 b, which may be hundreds or even thousands ofvolts AC, is rectified by a pair of diodes D51 and D52 and then storedin a capacitor C51, charging the capacitor C51 to greater than 500volts. The stored energy is: ½CV2 where C=0.33 uF 500V−0.04125 joules.FIG. 54 illustrates a series of pulses produced by the oscillator aloneconnected to a 100-bulb light string with the first and last bulbsremoved.

As it may take several seconds for the capacitor C51 to fully charge,the light-emitting diode LED51 indicates when the proper charge has beenestablished. As the voltage on C51 reaches its maximum value, a voltagedivider formed by a pair of resistors R55 and R56 starts to bias “on” anN-channel MOSFET Q52. (The resistors R55 and R56 also provide a leakagepath for the capacitor C51.) The LED51 increases in brightness when theVg-s threshold of Q52 is reached and becomes brighter as the Vg-sincreases. A capacitor C52 is charged through the resistor R55 andprovides a time delay to insure a full charge on the capacitor C51. Q52and a resistor R57 are in parallel with the resistor R51 and thus lowerthe total resistance when Q52 conducts, thereby increasing the currentthrough LED51 to make it glow brighter. The resistor R57 serves as acurrent-limiting resistor while Q52 is conducting. When the output ofthe red LED51 reaches constant brightness, the output voltage is at itsmaximum.

When the charge on the capacitor C51 builds up to a threshold level,e.g., 500 volts, it reaches the firing voltage of a gas-filled, ceramicspark gap SG50, thereby applying the voltage to the failed bulb in thelight string and reducing the intensity of LED51. This voltage continuesto build until it produces at least a partial breakdown of thedielectric material in the malfunctioning shunt. If the LED52 is notilluminated, the switch S50 is held in the depressed position, whichcauses the charging and discharging cycle to repeat. This is continuedfor as long as S10 is depressed, and if the LED52 is still notilluminated, the user pulls the trigger 314 the next time the LED51reaches maximum brightness. This produces the concurrent pulses fromboth the piezoelectric device 311 and the battery-powered circuit. Whenthe device is turned off, any remaining charge on the capacitor C51 isdischarged through a resistor R54.

The high-voltage pulse from the piezoelectric device produces an arcacross the spark gap 362, thereby creating a discharge path for theenergy stored in the capacitor C51. If the resulting pulse from thepiezoelectric device 311 (or combined pulse from both the piezoelectricdevice 311 and an MOV) fixes the malfunctioning shunt, the LED52 isilluminated. If the LED52 is not illuminated, the trigger 314 may bepulled several more times to produce successive combined pulses. If thegreen LED51 is still not illuminated, the user may proceed to thedetection modes to attempt to identify the failed bulb or other defect,so that the bulb can be replaced or the other defect repaired.

A first detection mode causes a failed bulb to glow by supplying thelight string with the pulse from only the battery-powered circuit,independently of the piezoelectric device 311, by again depressing theswitch S50. Again the pulse-triggering device breaks down when thevoltage builds up to a threshold level, and then a high voltage will becontinually applied to the failed bulb or other discontinuity as long asthe switch is held down. This causes a failed bulb of the third typedescribed above to glow, so that it can be visually identified andreplaced.

A second detection mode causes a failed bulb to flash by generatingconcurrent pulses from the piezoelectric device 311 and thebattery-powered circuit. As described previously, this combined pulse isproduced by pressing switch S10 until LED51 illuminates, and thenpulling the trigger 314 (as shown in FIG. 32) to activate the device311. This causes a failed bulb of the fourth type described above toflash, so that it can be visually identified and replaced.

The circuit of FIG. 35 permits the user to quickly locate and replace afailed bulb without attempting to fix the shunt associated with thatbulb, or the user can first attempt to fix a malfunctioning shunt withhigh-voltage pulses from either or both of two different sources. If theuser does not see a bulb glow or flash the first time a pulse isgenerated, the pulses may be repeated until a glow or flash is detected.

If desired, the output voltage of the battery-powered circuit can beincreased by increasing the turns ratio between the secondary andprimary windings of the step-up transformer T50. Also, the circuitparameters may be selected so that the gas-filled spark gap or othertriggering device does not break down until the piezoelectric device 311is also triggered.

FIG. 36 a is a schematic diagram of a circuit that can be used as analternative to the circuit of FIG. 34 for identifying the location of afailed bulb in a light string. FIG. 36 b shows the battery B that isused to provide the voltage V_(cc) that powers the buzzer 353 and LED61in the circuit of FIG. 36 a whenever the switch S61 is closed. Thecircuit in FIG. 36 a is the same as the circuit in FIG. 34 except that(1) the circuit of FIG. 36 a eliminates LED42, the sensitivity switchS42 and its associated capacitor C45, and the sub-circuit that includesthe transistor Q42, and (2) the resistor R41 is replaced by anelectrolytic capacitor C66(e.g., 4.7 μF). It has been found that the useof the electrolytic capacitor C66 provides more stable and reliableoperation over a fixed range of distances between the probe and thewires of the light string. That is, the response of the buzzer 353remains the same for different light strings, and different ambientconditions, as long as the probe is held within ⅛ to one inch from thewires of the light string.

Another alternative to the circuit of FIG. 34 is the circuit shown inFIGS. 37 a and 37 b, which is a sample-and-hold differential detector.Referring first to the block diagram in FIG. 37 a, the AC electrostaticfield around an energized light string is detected by a capacitivesensor comprising a pair of spaced parallel plates 450 and 451 connectedto the positive and negative inputs of a differential amplifier 452. Theplates 450 and 451, which are typically about 0.5 inch square, arelocated on opposite sides of the light string and pick up the AC fieldas they are moved along the length of the light string. When the sensoris close to a failed bulb, the field strength decreases by about 50%,and thus the purpose of the detection circuit is to detect that drop infield strength.

Before scanning a light string, the sensor is positioned near the plugend of the wires, and a “sample” switch 453 is closed momentarily tostore a sample of the field strength at that location, where the fieldstrength should be at its maximum. More specifically, the output of thedifferential amplifier 452 is passed through a rectifier 454 and storedin a conventional sample-and-hold circuit 455 when the switch 453 isclosed. This stored sample is then used as a reference signal input to acomparator 456 during the scanning of the light string. The other inputto the comparator is the instantaneous rectified output of the amplifier452, which is supplied to the comparator whenever a “test” switch 457 isclosed. If desired, the stored sample may be scaled by a scaling circuit458 before it is applied to the comparator 456. For example, the storedsample may be scaled by about ¾ so that the threshold value used in thecomparator is about 75% of the maximum field strength, as determined bythe sample taken near the plug end of the wires of the light string.

The comparator 456 is designed to change its output when the actualfield strength falls below about 50% of the threshold value, indicatingthat the sensor is adjacent a bad bulb. An alarm or indicator 459responds to the change in the output of the comparator 456 to produce avisible and/or audible signal to the user that a bad bulb has beenlocated. The sample level can also be taken with the plug in theunpolarized position so that the change at the defective bulbcorresponds to an increase in the level instead of a decrease. Thethreshold value can also be set so that this increase above the samplelevel triggers the alarm or indicator. The two approaches can also becombined so that the customer does not need to check the polarity of theplug before testing the string. The sample is taken and then circuitrylooks for a change, either up or down, and either will trigger theindicator.

FIG. 37 b is a schematic diagram of a circuit for implementing thesystem illustrated by the block diagram of FIG. 37 a. The differentialamplifier 452 includes a capacitor C70 in parallel with its feedbackresistor R70 to roll off the high frequency response and thereby preventerratic operation from noise and RF signals propagating along the powerline. When the “sample” switch 453 is momentarily closed, the output ofthe differential amplifier is passed through a diode D70 to anelectrolytic capacitor C71. The diode D70 functions as a half waverectifier, while the capacitor C71 stores the peak level of the signalfor use as a threshold signal in the comparator 456. Closure of the“sample” switch 453 also sends a pulse through a capacitor C73 to thebase of a transistor Q70 to turn the transistor on for about 0.01 secondto discharge the previously stored sample before the new sample isstored in the capacitor C71.

As the sensor plates 450, 451 are moved along the light string, the“test” switch is closed to supply the rectified output of thedifferential amplifier 452 to a current-value storage filter formed byan electrolytic capacitor C72 and a resistor R70 connected in parallelwith each other between the switch 457 and ground. The value stored inthe filter is supplied to the positive input of the comparator 456 whichcompares that value with the threshold value from the electrolyticcapacitor C71. When the current value falls below a predetermined value,the comparator output changes to activate the alarm device 459.

A variety of different circuits may be used to generate signals (whichin some embodiments may be pulsed signals) of a magnitude greater thanthe standard AC line voltage to fix a malfunctioning shunt. One suchalternative circuit is illustrated in FIG. 38, in which a battery B80supplies DC power to a blocking oscillator 500 to generate ahigh-voltage AC signal that is rectified by a pair of diodes D80 and D81and then used to charge a capacitor C80. When the capacitor C80 chargesto a predetermined level, it discharges through a resistor R80 and aspark gap device SG80 (such as a gas discharge or neon tube) to producethe high-voltage pulses that are applied to a light string plugged intoa socket 501. The resistor R80 functions to stretch the pulses, whilethe spark gap device SG30 controls the pulse shape and voltage level. Ithas been found that the addition of a resistance (e.g., ˜1000 ohms) inseries with the discharge path of the capacitor into the light stringincreases the rate of success in fixing malfunctioning shunts.

Operation of the oscillator 500 is initiated by closing a switch S80that supplies power from the battery B80 to the primary winding T80 aand an auxiliary winding T80 b of a transformer T80. A transistor Q80has its collector and base connected to the two windings T80 a and T80b, respectively, and its emitter is connected to the negative side ofthe battery B80. A resistor R82 is connected in series with T80 b tosupply base current to Q80 from T80 a and T80 b. The blocking oscillatoroperates in the conventional manner, producing a stepped-up AC signal inthe secondary winding T80 c of the transformer as long as the switch S80remains closed. A filtering capacitor C82 is connected across thesecondary winding T80 c.

FIG. 39 illustrates a current-fed sinusoidal wave converter that may beused as an alternative to the circuit of FIG. 38. Power is supplied tothe converter from a battery B90 via inductor L90 whenever a switch S90is closed. The battery B90 is connected in parallel with an electrolyticcapacitor C90 that stores energy from the battery for producing thedesired high-voltage signal. The desired sinusoidal signal is producedby a conventional sinusoidal-wave generating circuit that includes apair of transistors Q90 and Q91 connected to a pair of primary windingsT90 a and T90 b of a transformer T90. A capacitor C91 is connectedacross the winding T90 a. As long as the switch S90 remains closed, thetransistors Q90 and Q91 are repetitively turned on and off, with one ofthe transistors always being on while the other is off, so as to producea sinusoidal output signal in the secondary winding T90 c of thetransformer T90. This sinusoidal output is applied directly to a lightstring plugged into a socket 600 connected to opposite ends of thewinding T90 c.

FIG. 41 illustrates a circuit that uses a battery B110 as a power sourceand a conventional blocking oscillator consisting of the NPN transistorQ110; a transformer T110 with a primary winding T110 a, a feedbackwinding T110 b, and a secondary winding T110 c; and a resistor R110. Thetransformer T110 is a step-up transformer with a secondary winding T110c consisting of many turns to raise the peak AC voltage to about 1000volts, which is rectified by a pair of diodes D110 and D111 and used tocharge a capacitor C110(e.g., 0.1 μF) to a voltage determined by thebreakdown voltage of the defective shunt in the failed bulb. When thisvoltage is reached, typically 500 to 1000 V, the oxide or otherinsulation on the shunt breaks down and the voltage across the bulbfalls abruptly to a low value as a heat-producing discharge occursbetween the shunt and the filament support wires. This discharge hasbeen shown to cause breakdown and burn-through of the oxide in amalfunctioning shunt in a light string plugged into a socket 801,rendering the shunt conductive and allowing the light string to functionnormally. Shaping the pulse by the use of inductive, capacitive,resistive and/or active component elements has been shown to improve theeffectiveness of the pulse. For example, increasing the length of thedischarge current pulse with the resistor R110 (e.g., 1000 ohms)produces a statistically significant increase in the number ofmalfunctioning shunts that are rendered conductive. As somemalfunctioning shunts are not true open circuits but rather comprise ahigh resistance which inhibits charging of the capacitor C110, theaddition of a spark gap in series with the resistor R110 allows fullcharging of the capacitor C110 before current is delivered to the lightstring.

FIG. 42 illustrates a circuit that uses the reactance of a transformerT120 to limit current from an AC power source to safe values (about 10to 30 mA) and cause breakdown of and subsequent shorting of amalfunctioning shunt by virtue of the voltage and current applied overseveral AC line cycles. The transformer windings T120 a and T120 b arechosen to form a step-up transformer that applies a higher-than-ratedvoltage to a light string plugged into a socket 900, to cause themalfunctioning shunt to conduct. The exact duration and peak current andother characteristics of the high voltage can vary widely and stillaccomplish the same function.

FIG. 43 depicts the use of a conventional Cockroft-Walton voltagemultiplier array in another AC line-operated configuration for repairinga malfunctioning shunt in a light string plugged into a socket. Thethree-stage multiplier 950, formed by diodes D130-D135 and capacitorsC130-C135 and connected to the AC source boosts the voltage to about900-1000 volts, and discharges through a resistor R130 when thebreakdown voltage of the malfunctioning shunt is reached. Connectedbetween the AC source and a socket 952 for receiving the plug of thelight string, is a pair of diodes D136 and D137 that are reverse biased(and therefore non-conductive) by the high voltage DC, but conduct onpositive half cycles of the AC line voltage to immediately illuminatethe string of lights dimly once the initial breakdown occurs, thusgiving the operator fast feedback on the success of the repairprocedure.

Another preferred embodiment of the invention is illustrated in FIGS.44-52. In this embodiment the overall shape of the housing has beenmodified to form a generally L-shaped body 1000 resembling the profileof a futuristic handgun. In the illustrative embodiment, the body 1000is made in three molded plastic parts 1000 a-1000 c fastened together bya few détente latches and screw sockets molded as integral parts of theinterior surfaces of the body parts, and screws threaded onto the moldedsockets.

The trigger 1001 protrudes from the housing 1000, having no obstructionson the free side 1001 a of the trigger 1001 in order to give the usereasy access. A metal bulb pulling tool 1002 is located at the top of thehousing 1000 in front of the trigger 1001 and inside a wire loop 1003which forms the probe P of the circuit. A plastic cover 1004 formed bythe housing 1000 encases the wire loop 1003 and forms a guard extendingalong and slightly spaced from the leading edge of the bulb pulling tool1002 to protect the user from the sharp edges on the tool.

A bulb-testing socket is formed by a hole 1005 in the top wall of thehousing 1000, directly behind the bulb pulling tool 1002, and a pair ofspring contacts 1006 and 1007 mounted on a printed circuit board (PCB)1008 directly beneath the hole 1005. To accommodate light bulbs withlong bases, an aperture 1012 (see FIG. 52) is formed in the PCB 1008between the two spring contacts 1006 and 1007. The contacts 1006 and1007 are connected via the PCB 1008 to a second pair of spring contacts1009 and 1010 mounted on the PCB 1008 for receiving a battery 1011 (seeFIG. 47 a) or stack of batteries. When a bulb base is inserted throughthe hole 1005 into the space between the contacts 1006 and 1007, thebulb is connected to the battery B, causing the bulb to illuminate if itis a good bulb.

To facilitate battery replacement, the battery B is housed in a cavity1013 formed as an integral part of a molded plastic element 1014inserted in an opening 1015 at the handle end of the top wall of thehousing 1000 (see FIGS. 47 a and 50). The element 1014 serves as acombined removable battery holder and manually operable switch actuator.The ends of the battery B are exposed at opposite ends of the cavity1013 to engage the spring contacts 1009 and 1010 when the element 1014is inserted into the opening 1015. A lug 1016 depending from a flexibleactuator 1017 formed as an integral part of the rear portion of theelement 1014 engages a switch S1 mounted at the rear edge of the PCB1008 and forming part of a manually actuated battery test circuit. Whenthe actuator 1017 is pressed downwardly, it closes the switch S1 toilluminate the LED1 mounted on the PCB 1008 and extending upwardlythrough an aperture in the top wall of the housing 1000, indicating thata good battery is in place and the device is ready to operate. A latch1018 on the front edge of the element 1014 mates with an aperture 1018 ain the opposed wall of the housing to hold the element 1014 in place inthe housing 1000.

All the other elements of the field-detecting and signaling circuit ofFIG. 36 a, except the buzzer 53, are mounted on the PCB 1008, which iscaptured in the housing 1000 above a longitudinal septum 1019. A pair ofwire leads 53 a and 53 b connect the PCB 1008 to the buzzer 53 mountedin the interior of the cover 1004. The piezoelectric pulse generator1020 is mounted beneath the septum 1019, so that the septum shields thePCB and its circuitry from any arcs that might be produced by thepiezoelectric device 1020 if the trigger 1001 is pulled when no lightstring is plugged into the housing 1000. An electrical receptacle 1021for receiving the prongs of the plug on a light string is formed in thelower front wall 1022 of the housing 1000, below and to the rear of thetool 1002. A pair of metal sockets 1023 and 1024 receive the two prongsof the plug, and the two sockets 1023 and 1024 are connected to oppositesides of the piezoelectric pulse generator 1020. The trigger 1001 ismounted for reciprocating sliding movement in the housing 1000 directlybeneath the piezoelectric device 1020 and in direct engagement with themovable striker of the piezoelectric device. The internal return springin the piezoelectric device 1020 serves to return the trigger 1001 toits advanced position after every pull of the trigger.

In the preferred embodiment, the piezoelectric device 1020 comprises twopiezoelectric pulse generators connected in parallel with each other.Both generators are actuated in tandem by the same trigger 1001.

The handle 1025 of the housing 1000 forms a storage area 1026 that isconveniently divided into three compartments 1026 a-c for separatestorage of fuses and different types of bulbs. The storage compartmentsare covered by a removable lid 1027 which has a pair of rigid hooks 1028and 1029 on its upper edge for engaging mating lugs 1030 and 1031 on thewall of the central compartment 1026 b. The opposite edge of the lid1027 forms a flexible latch 1032 that releasably engages mating lugs1033 on the wall of the central compartment 1026 b.

FIG. 55 is another schematic diagram of a power supply for converting astandard 120-volt, 60-Hz input at terminals 2161, 2162 into a 24-volt ACoutput at terminals 2163, 2164 and 2165, 2166. This circuit uses aswitching power supply to deliver a low-voltage, high-frequency PAMsignal while also providing the following features for the lightstrings:

-   -   continuous dimming capability from very low light level to full        light level,    -   multi-level dimming capability,    -   energy-saving and minimum-light-setting features,    -   soft-start feature to increase the lamp life,    -   soft start feature to reduce inrush current in the circuit, and    -   low cost with multi-feature lighting.

The AC input from the terminals 2161, 2162 is supplied through a fuseFH1 to a diode bridge DB2021 consisting of four diodes to produce afull-wave rectified output across buses 2167 and 2168, leading to a pairof capacitors C2023 and C2024 and a corresponding pair of transistorsQ2021 and Q2022 forming a half bridge. The input to the diode bridgeDB2021 includes a passive component network consisting of C2003, C2004,C2006, C2007, L2001, L2004 and RV2001 which are part of the radiofrequency interference and line noise filtering circuitry. CapacitorsC2025 and C2026 are connected in parallel with capacitors C2023 andC2024, respectively, to provide increased ripple current rating andhigh-frequency performance. The capacitors C2023 and C2024 may beelectrolytic capacitors while capacitors C2025 and C2026 are film-typecapacitors offering high-frequency characteristics to the parallelcombination.

The capacitors C2023, C2024 form a virtual center tap. One end of theprimary winding T_(p) of an output transformer T2022 is connected to apoint between the two capacitors. The secondary winding T_(S) of thetransformer T2022 is connected to the output terminals 2163, 2164 and2165, 2166, through series inductors L2002 and L2003 (along with C2014,C2015, C2016 and R2016) which act as filters to minimize electromagneticinterference. The output terminals receive one or more plugs on the endsof light strings.

An integrated circuit driver U2001, such as a IR21571D controlleravailable from International Rectifier, controls the switching frequencyof oscillation and other features indicated above. The power supplyV_(cc) for the driver U2001 is derived from the DC bus through aresistors R2001 and R2002 to an internal zener diode. The deviceincludes protection elements which prohibit starting oscillation(operation) until the power supply voltages are in tolerance and ifthere is a fault which interferes with the proper sequencing of voltagesV_(DC), V_(CC), and V_(SD). Diodes D2002, D2003, D2004 and capacitorsC2009, C2010 and C2011 provide a boot-strap mechanism for powering theIC. C2012 and C2018 provide bulk storage to start the controller atpower up.

The frequency of oscillation of the controller is determined by thetotal resistance connected to ground from pin 2004 of the controllerU2001 and a capacitor C2013 connected across pin 2006 and ground of thecontroller U2001. The two outputs of the U2001 pins 2011 and 2016 areconnected to the gates of the MOSFETs Q2021 and Q2022. A resistor R2008limits the gate current of the MOSFET Q2021. A resistor R2015 limits thegate current of the MOSFET Q2022.

When power is applied to the circuit, the voltage developed on the bus2167 causes voltage to be applied to U2001 V_(CC), V_(DC), and V_(SD).This causes the U2001 to start oscillating and start driving thehalf-bridge transistors Q2021 and Q2022 alternately. This appliesvoltage across the primary winding T_(P) of the transformer T2021, whichin turn applies voltage across the secondary winding T_(S) of thetransformer, which is applied to the load.

The rectified output of the DC bus 2167 is applied to the Vcc and V_(DC)pins of the controller U2001 through resistors R2001 and R2002. Aninternal zener diode and capacitors C2018 and C2012 maintain theoperating voltages for the controller. A voltage divider consisting of athermistor TH2001 and R2005 set the value V_(SD). The controller usesthese three voltages to determine the state of the power bus 2167 toprevent operation when the power bus has collapsed.

The preset output voltage is set by the turns ratio of the outputtransformer T2022. A limited dimming control is achieved by adjustingthe resistance that appears between pins 2006 and 2007 of controllerU2001. This resistance controls the amount of dead time for the outputFETs which reduces the RMS value of the output voltage of T2002 andthereby reducing the intensity of the light strings connected toterminals 2163, 2164 and 2165, 2166

The dimming feature can be used to provide different fixed light levels,such as a low light output, an energy-saving output, or a full-lightoutput. These three light levels can be achieved by use of three fixedresistors in place of the potentiometer R2014. The three resistorsettings can be selected by use of a three-position switch. A low-lightoutput corresponds to a maximum output dead time, and a full-lightoutput corresponds to minimum dead time. An energy-saving outputcorresponds to an intermediate light level such as a 75% light output.

The controller has an additional control pin (SD) which can be used as athermal shutdown control to protect the power supply from overheating.As the air temperature in the unit rises, the value of TH2001 willdecline until the voltage appearing at pin 2009 of U2001 rises above theshut down value of approximately 2.0 volts.

The particular embodiment illustrated in FIG. 55 is a half bridgecircuit as an example but it will be understood that the features ofthis circuit can be incorporated in other topologies such as flyback,forward, cuk, full bridge or other power converters, including isolatedas well as non-isolated power converter designs.

1. A string of decorative lights comprising a power supply having aninput adapted for connection to a standard residential electrical poweroutlet, said power supply including circuitry for converting thestandard residential voltage to a low-voltage output, a pair ofconductors connected to the output of said power supply for supplyingsaid low-voltage output to multiple decorative lights, and multiplelights connected to said conductors along the lengths thereof, each ofsaid lights, or groups of said lights, being connected in parallelacross said conductors.
 2. A string of decorative lights as set forth inclaim 1 wherein each of said lights is about a half-watt bulb.
 3. Astring of decorative lights as set forth in claim 1 wherein each of saidlights requires a voltage or about 6 volts or less
 4. A string ofdecorative lights as set forth in claim 1 wherein said lights areconnected in parallel across said conductors in parallel groups of twoto five lights per group, the lights within each group being connectedin series.
 5. A string of decorative lights as set forth in claim 1wherein said standard residential voltage is 120 volts and approximately100 6-volt lights are connected to said conductors.
 6. A string ofdecorative lights as set forth in claim 1 wherein said low-voltageoutput is DC.
 7. A string of decorative lights as set forth in claim 1wherein said low-voltage output is AC.
 8. A string of decorative lightsas set forth in claim 1 wherein said low-voltage output is less thanabout 30 volts.
 9. A string of decorative lights as set forth in claim 1wherein said power supply comprises an electronic transformer.
 10. Astring of decorative lights as set forth in claim 1 wherein said powersupply comprises a switching power supply.
 11. A string of decorativelights as set forth in claim 1 wherein said power supply converts thestandard residential frequency to a higher frequency output.
 12. Astring of decorative lights as set forth in claim 11 wherein said higherfrequency is in the range from about 10 KHz to about 150 KHz.
 13. Astring of decorative lights as set forth in claim 1 wherein saidconductors are connected to a fixed number of said lights so as toprovide a fixed load on said power supply.
 14. A string of decorativelights as set forth in claim 1 wherein each of said lights includesmeans for shunting the light in response to a failure of the light. 15.A decorative lighting system, said system comprising a power supplyhaving an input adapted for connection to a standard residentialelectrical power outlet, said power supply including circuitry forconverting the standard residential voltage to a low-voltage output, aplurality of pairs of conductors connected to the output of said powersupply for supplying said low-voltage output to multiple sets ofdecorative lights, and multiple lights connected to each pair of saidconductors along the lengths thereof, each of said lights, or groups ofsaid lights, being connected in parallel across each of said pairs ofconductors.
 16. A decorative lighting system as set forth in claim 15wherein each of said lights is about a half-watt bulb.
 17. A decorativelighting system as set forth in claim 15 wherein each of said lightsrequires a voltage or about 6 volts or less
 18. A decorative lightingsystem as set forth in claim 15 wherein each of said pairs of conductorshas multiple groups of said lights connected in parallel across theconductor pair, each of said parallel groups including two to fivelights connected in series within the group.
 19. A decorative lightingsystem as set forth in claim 15 wherein said standard residentialvoltage is 120 volts and approximately 100 6-volt lights are connectedto each of said pairs of conductors.
 20. A decorative lighting system asset forth in claim 15 wherein said low-voltage output is DC.
 21. Adecorative lighting system as set forth in claim 15 wherein saidlow-voltage output is AC.
 22. A decorative lighting system as set forthin claim 15 wherein said low-voltage output is less than about 30 volts.23. A decorative lighting system as set forth in claim 15 wherein saidpower supply comprises an electronic transformer.
 24. A decorativelighting system as set forth in claim 15 wherein said power supplycomprises a switching power supply.
 25. A decorative lighting system asset forth in claim 15 wherein said power supply converts the standardresidential frequency to a higher frequency output.
 26. A decorativelighting system as set forth in claim 25 wherein said higher frequencyis in the range from about 10 KHz to about 150 KHz.
 27. A decorativelighting system as set forth in claim 15 wherein each of said pairs ofconductors is connected to a fixed number of said lights so as toprovide a fixed load on said power supply.
 28. A decorative lightingsystem as set forth in claim 15 wherein each of said lights includesmeans for shunting the light in response to a failure of the light. 29.A method of powering a string of decorative lights, said methodcomprising converting a standard residential electrical voltage to alow-voltage, and supplying said low-voltage to a pair of parallelconductors having multiple decorative lights connected to saidconductors along the lengths thereof, each of said lights, or groups ofsaid lights, being connected in parallel across said conductors.
 30. Amethod of powering a string of decorative lights as set forth in claim29 wherein each of said lights is about a half-watt bulb.
 31. A methodof powering a string of decorative lights as set forth in claim 29wherein each of said lights requires a voltage or about 6 volts or less32. A method of powering a string of decorative lights as set forth inclaim 29 wherein said lights are connected in parallel across saidconductors in parallel groups of two to five lights per group.
 33. Amethod of powering a string of decorative lights as set forth in claim29 wherein said standard residential voltage is 120 volts andapproximately 100 6-volt lights are connected to said conductors.
 34. Amethod of powering a string of decorative lights as set forth in claim29 wherein said low-voltage output is DC.
 35. A method of powering astring of decorative lights as set forth in claim 29 wherein saidlow-voltage output is AC.
 36. A method of powering a string ofdecorative lights as set forth in claim 29 wherein said low-voltageoutput is less than about 30 volts.
 37. A method of powering a string ofdecorative lights as set forth in claim 29 wherein an electronictransformer is used in the conversion of said standard residentialelectrical voltage to a low voltage.
 38. A method of powering a stringof decorative lights as set forth in claim 29 wherein a switching powersupply is used in the conversion of said standard residential electricalvoltage to a low voltage.
 39. A method of powering a string ofdecorative lights as set forth in claim 29 wherein the standardresidential frequency is converted to a higher frequency output.
 40. Amethod of powering a string of decorative lights as set forth in claim39 wherein said higher frequency is in the range from about 10 KHz toabout 150 KHz.
 41. A method of powering a string of decorative lights asset forth in claim 29 wherein a fixed load is maintained on saidconductors by limiting the number of lights connected to said conductorsto a fixed number.
 42. A method of powering a string of decorativelights as set forth in claim 29 which includes the step of shunting eachof said lights in response to a failure of that light.
 43. A string ofdecorative lights comprising: a plurality of elongated electricalconductors having multiple electrical lamps connected thereto atintervals along the lengths of the conductors, a small storagecompartment for storing spare components for use in said string ofdecorative lights, a movable closure for opening said storagecompartment to permit access to the spare components stored therein, andfor closing the compartment during storage of the spare components, andmeans for attaching said storage compartment to said string ofdecorative lights so that the spare components stored therein areconveniently accessible when needed to replace a component in said lightstring.
 44. The decorative light string of claim 43 which includes aplug or receptacle on at least one end of said string, and said storagecompartment is attached to said light string by being formed as a partof said plug or receptacle.
 45. The decorative light string of claim 43which includes a receptacle on at least one end of said string, and saidstorage compartment is attached to said light string by prongsprojecting from an exterior surface of said storage compartment andpositioned and dimensioned to fit into said receptacle.
 46. Thedecorative light string of claim 43 wherein said storage compartment isdivided into sub-compartments for segregated storage of differentcomponents.
 47. The decorative light string of claim 43 wherein saidmovable closure includes a cover and a hinge connecting said cover tosaid storage compartment to allow the cover to pivot about the hinge toselectively open and close the compartment.
 48. The decorative lightstring of claim 43 further comprising locking means for selectivelymaintaining said movable closure in a closed position.
 49. Thedecorative light string of claim 43 wherein said storage compartmentincludes at least two opposite interconnected walls forming channelsadapted to slidably receive said movable closure for opening and closingsaid compartment.
 50. The decorative light string of claim 43 whereinsaid storage compartment includes a wall forming a first opening adaptedto receive in frictional engagement a base of an electrical lamp, toassist in removing the electrical lamp from a socket.
 51. The decorativelight string of claim 50 wherein said movable closure includes a domedportion defining a second opening aligned with said first opening toreceive the base of the electrical lamp in frictional engagement toassist in removing the electrical lamp from a socket.
 52. The decorativelight string of claim 50 further comprising means to cover said firstopening when no bulb is placed therein for removal.
 53. The decorativelight string of claim 51 further comprising means to cover both saidfirst and second openings when no bulb is placed therein for removal.54. A method of storing spare components for use in a string ofdecorative lights, said method comprising: placing said spare componentsin a small storage compartment having a movable closure for opening thecompartment to permit access to the spare components stored therein, andfor closing the compartment during storage of the spare components, andattaching said storage compartment to said string of decorative lightsso that the spare components stored therein are conveniently accessiblewhen needed to replace a component in said light string.
 55. The methodof claim 54 wherein said light string includes a plug or receptacle onat least one end of the string, and said storage compartment is attachedto said light string by being formed as a part of said plug orreceptacle.
 56. The method of claim 54 wherein said light stringincludes a receptacle on at least one end of the string, and saidstorage compartment is attached to said light string by prongsprojecting from an exterior surface of said storage compartment andpositioned and dimensioned to fit into said receptacle.
 57. The methodof claim 54 wherein said storage compartment is divided intosub-compartments for segregated storage of different components, andsaid different components are placed in different ones of saidsub-compartments.